Patent Application
20130157876
The present application includes and incorporates by reference the attached Table 2.
The instant application contains a Sequence Listing which has been submitted in ASCII format via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Feb. 14, 2013, is named 2927US_SequenceListing_ST25.txt and is 542,906 bytes in size.
1. Field of the Invention
The present embodiments relate to the design and implementation of a microarray-based assay and array system for detecting specific target genes from organisms permitting microbial identification and profiling of antibiotic resistance and methods of use of the assay and array system thereof.
2. Description of the Related Art
A DNA microarray (also commonly known as gene or genome chip, DNA chip, or gene array) is a collection of microscopic DNA spots attached to a solid surface, made of such materials as glass, plastic or silicon and forming an array. The solid surface can be planar or other surface shapes, such as microbeads, etc. The affixed DNA segments are known as probes (although some sources will use different nomenclature), thousands of which can be used in a single DNA microarray. Microarrays may be used to detect specific genes and to measure their expression which is relevant to many areas of biology and medicine, such as studying treatments, disease, and developmental stages. For example, microarrays can be used to identify disease genes by comparing gene expression in diseased and normal cells.
Healthcare-associated infections [HAIs] are a worldwide problem affecting diverse groups of patients. A major challenge in fighting HAIs is the rising tide of antimicrobial resistance. Nonclinical environments are the natural origin of most antibiotic resistance elements; however, the use of broad-spectrum antibiotics in the clinical setting places significant selective pressure on microorganisms, altering the functional role of these elements.
There is a need to provide a sensitive and specific molecular tool for rapid, culture-independent identification of microbial species present in a clinical sample as well as providing information on the antibiotic resistance potential of these strains. This is relevant to research applications, but particularly pertinent for clinical applications. Specifically, there is currently no clinical diagnostic tool available that can simultaneously identify a large panel of pathogenic microorganisms (at least 44 species) and their associated antibiotic resistance genes within a time frame that will permit therapeutic antimicrobial treatment strategies to dramatically impact patient outcomes. Though it has been determined that appropriate (meaning efficacious against the infectious agent) and adequate (meaning sufficient concentrations to effect a >90% bactericidal rate) administration of antibiotics within 24 hours of presentation with infection significantly improves patient outcomes, to date no current technique simultaneously allows organism detection and antibiotic resistance profiling for a multitude of nosocomial pathogenic agents in one assay within 10-24 h. Current clinical laboratory tests are primarily culture-based or, if molecular, rely upon fluorescence in situ hybridization or PCR amplification alone (which are typically single species specific). [(1) PNA-FISH, AdvanDx (2) Amplified MTD, Gen-Probe (3) IDI-MRSA, Cepheid] These detect only a limited number of infecting pathogens and/or specific antibiotic resistance determinants in clinical samples. Their detection sensitivity is not at strain level. Almost all of these tests are each limited to a couple of pathogens and resistance determinants. Each one is laborious and running a battery of these tests make them expensive and time consuming, and in many cases do not satisfy the requirements of clinical timelines to affect treatment decisions.
Early work has already demonstrated the potential of microarray methods for detection of pathogenic bacteria and their associated resistance elements and virulence factors (Wilson W J, Strout C L, DeSantis T Z et al. Sequence-specific identification of 18 pathogenic microorganisms using microarray technology. Mol Cell Probes 2002; 16:119-27). Anthony et al. used universal PCR primers to amplify 23S ribosomal DNA from bacteria in clinical blood cultures, followed by hybridization to a microarray with species-specific sequences for 95 bacterial and fungal pathogens (Anthony R M, Brown T J, French G L. Rapid diagnosis of bacteremia by universal amplification of 23S ribosomal DNA followed by hybridization to an oligonucleotide array. J Clin Microbiol 2000; 38:781-8). Of 158 culture-positive clinical specimens, 125 (80%) were correctly identified using this approach. Discrepancies were due to inadequate target coverage on the microarray, false-negative PCR amplifications and false-negative cultures.
Other groups have developed microarray techniques to accurately characterize the presence of antimicrobial resistance elements in microorganisms. Lee et al. developed a DNA chip to detect a variety of different classes of beta-lactamase genes from Gram-negative bacteria, demonstrating an ability to detect the presence of resistance genes in as little as a single organism (Lee Y, Lee C S, Kim Y J et al. Development of DNA chip for the simultaneous detection of various beta-lactam antibiotic-resistant genes. Mol Cells 2002; 14:192-7). The potential of microarrays to detect single nucleotide polymorphism variants in antibiotic resistance genes was demonstrated by Grimm et al. in their study of the common Gram-negative beta-lactamase TEM-1 (Grimm V, Ezaki S, Susa M et al. Use of DNA microarrays for rapid genotyping of TEM beta-lactamases that confer resistance. J Clin Microbiol 2004; 42:3766-74). This study correctly identified different TEM variants in Escherichia coli, Enterobacter cloacae, and Klebsiella pneumoniae. Frye et al. developed a microarray with probes for 94 antimicrobial resistance genes (Frye J G, Jesse T, Long F et al. DNA microarray detection of antimicrobial resistance genes in diverse bacteria. Int J Antimicrob Agents 2006; 27:138-51). When tested against 51 Gram-negative and Gram-positive bacteria, 61 resistance genes were detected, with good agreement between the presence of genes for resistance and phenotypic susceptibility results.
The most advanced work to date in development of a clinically useful microarray for rapid detection of pathogens and antimicrobial resistance was reported by Cleven et al. (Cleven B E, Palka-Santini M, Gielen J et al. Identification and characterization of bacterial pathogens causing bloodstream infections by DNA microarray. J Clin Microbiol 2006; 44:2389-97.). This group designed a microarray platform to perform pathogen identification and detection of resistance elements in Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Identification of all three species from blood culture samples was 100%, and there was excellent agreement between resistance gene probes and results of phenotypic susceptibility testing for Staphylococcus aureus.
One limitation of current methods for detection of antimicrobial resistance genes via DNA microarrays is the inability to predict expression levels among the identified genes. While the presence of antimicrobial resistance genes in many organisms correlates well with phenotypic resistance, some resistance genes may be chromosomally located and have variable effect on resistance based on their level of expression. Chromosomally encoded resistance genes are common among wild-type isolates of Gram-negative bacteria such as P. aeruginosa, Enterobacter, and Acinetobacter (Hancock R E. Resistance mechanisms in Pseudomonas aeruginosa and other nonfermentative Gram-negative bacteria. Clin Infect Dis 1998; 27 Suppl 1:S93-9). These genes usually encode either beta-lactamases or drug efflux pumps, and are expressed at low levels among drug-susceptible isolates. Mutations in the regulatory genes for these elements allows for their high-level expression, with subsequent phenotypic resistance (often to multiple drug classes). In order to characterize accurately the resistance profiles of these organisms, molecular methods such as microarrays must either be able to quantitatively measure gene expression or interrogate regulatory genes to determine the presence of mutations . . . .
In one embodiment, a computational pipeline to select both species-level identification and antibiotic resistance determinants for microbial detection, identification and antibiotic resistance phenotype prediction of important nosocomial pathogens. The focus was on 24 pathogenic organisms with clinical relevance and shown in Table 1.
In one embodiment, a robust, automated computational pipeline used to design a microarray of pathogen identification and antibiotic resistance elements. This array will facilitate the detection of organisms, including nosocomial pathogens and their resistance profiles in a clinical setting. In addition, the tool will have applications in epidemiological studies, given its capability to provide virtual real-time information on strain identity and resistance profile, it may be used during infectious outbreaks to track dissemination and evolution of infectious agents.
In one embodiment, the array comprises probes to detect and identify specific nosocomial pathogens and their antibiotic resistance elements corresponding to at least the 24 pathogens in Table 1, wherein the probes are attached to a substrate or solid surface.
In other aspects, the probes which are 25 nucleotides long are used to detect and identify specific organisms and their antibiotic resistance elements.
In some aspects, the sample is an environmental sample. In other aspects, the environmental sample comprises at least one of soil, water, or atmosphere.
In some aspects, the sample is a processed or unprocessed food product. In other aspects, the food sample comprises at least one of meat, turkey, chicken and other poultry, milk, eggs, eggs products, dairy products, fresh or dried fruits and vegetables and their juices, grains, fish, seafood, pet food, baby food and infant formula,
In yet other aspects, the sample is a clinical sample. In still other aspects, the clinical sample comprises at least one of tissue, skin, stool, bodily fluid, or blood.
In another aspect, the sample is a bacterial isolate.
Some embodiments relate to a method of detecting an organism including applying a pool of DNA fragments amplified from genomes extracted from the sample to the array system which includes a microarray that comprises probes that specifically target genomic regions specific to an organism and their antibiotic resistance elements.
In some aspects, the plurality of organisms comprise bacteria.
In some aspects, the specific antibiotic resistance element and the organism (pathogenic or other) are detected in the sample.
Some embodiments relate to a method of fabricating an array system including identifying sequences conferring antibiotic resistance; clustering those sequences that target resistance determinants of clinical relevance; creating variant sequence fragments corresponding to these antibiotic resistance sequences; and fabricating said array system.
In one embodiment, the array system is a microarray system comprising: a resequencing microarray configured to simultaneously detect a plurality of organisms and antibiotic resistance elements in a sample, wherein the microarray comprises resequencing probes for organism identification, antibiotic resistance element detection, and detection of polymorphisms related to said antibiotic resistance, whereby said resequencing probes for organism detection can provide strain-level detection and identification of a pathogen in a sample and whereby said resequencing probes for antibiotic resistance elements and said resequencing probes for antibiotic resistance related polymorphisms provide for detection of emerging antibiotic resistance of pathogens in a sample
In one aspect, the invention provides a method for parallel detection and strain level-identification of a panel of more than 44 organisms, in parallel with antibiotic resistance profiling of said organisms comprising the steps of: (a) extraction of nucleic acids from a patient sample using a rapid optimized protocol; (b) amplifying a target loci in said nucleic acid using multiplex polymerase chain reaction; (c) pooling and labeling said target locus amplified products; (d) contacting the labeled amplified pool of products with a plurality of resequencing probes which target both the sense and anti-sense strands of the target loci represented in SEQ ID NOS:1-1323; (e) determining hybridization signal strength for each of said resequencing probes, wherein said determination identifies the specific sequence of the target locus, providing either strain level organism identification or single nucleotide polymorphism resolution or antibiotic resistance determinant sequence information. In some embodiments, the method further comprises in step (c) fragmenting the target locus amplified products.
In one embodiment, the array comprises probes to detect the presence of regulatory genes related to antibiotic resistance. In another embodiment, it comprises probes that cover promoter regions of genes involved in antibiotic resistance.
In some embodiments, the sample is a pulmonary sample, including but not limited to sputum, endotracheal aspirate, a bronchoalveolar lavage sample, or a swab of the endotrachea.
In some embodiments, the biosignature comprises the presence and antibiotic resistance elements profile of one or more nosocomial pathogens.
In another embodiment, the invention provides a method of diagnosis, prognosis, and/or prediction of an outcome of a subject. In one embodiment, the method comprises: (a) isolating nucleic acid material from a sample from said subject; (b) determining hybridization signal strength distributions across sets of 8 probes (4 based on sense strain, 4 on anti-sense strand) per nucleotide base interrogated in each target locus; (c) determining hybridization signal strengths for a plurality of different interrogation probes, each of which is complementary to a section within said loci; (d) using the hybridization signal strengths of probe sets to determine the sequence of the target locus. (e) using this information to determine the presence and antibiotic resistance repertoire of one or more target nosocomial pathogens; (f) defining therapeutic strategy based on the results of step (d); (g) classifying, diagnosing, prognosing, and/or predicting an outcome of said pulmonary condition based on the results of step (d). In some embodiments, the sample is a pulmonary sample, including but not limited to sputum, endotracheal aspirate, a bronchoalveolar lavage sample, or a swab of the endotrachea. In some embodiments, the method further comprises making a healthcare decision based on the results of step (d).
In one aspect, the invention provides a method of diagnosis, prognosis, and/or prediction of an outcome of a condition in a subject. In one embodiment, the method comprises: (a) obtaining a sample from a patient; (b) isolating nucleic acid material from said sample; (c) amplifying a target locus in said nucleic acid material; (d) contacting said target locus with a set of resequencing probes, wherein said set comprising 8 probes (4 probes based on the sense strand and 4 probes based on the anti-sense strand) per nucleotide base interrogated in each target locus; (e) determining hybridization signal strengths across the set of probes; (f) determining hybridization signal strengths for a plurality of different interrogation probes, each of which is complementary to a section within said target locus; (g) determining the sequence of the target locus by analysis of the hybridization signal strengths of the resequencing probe set; (h) comparing the target locus sequence with a set of known sequences to determine the presence and/or antibiotic resistance repertoire of one or more target organisms; (i) defining therapeutic strategy for said patient based on the results of step (h); (j) classifying, diagnosing, prognosing, and/or predicting an outcome of said condition based on the results of step (h). In some embodiments, the presence and antibiotic resistance profile is detected with a confidence level greater than 95%. Highly conserved target loci targeted with this invention include, but are not limited to, 16S rRNA gene, 23S rRNA gene, 5S rRNA gene, 5.8S rRNA gene, 12S rRNA gene, 18S rRNA gene, 28S rRNA gene, gyrB gene, rpoB gene, fusA gene, recA gene, coxl gene, nif13 gene, ahpC gene, embA gene, kasA gene, katG gene, parC gene, pncA gene and rlmN gene or RNA molecules derived therefrom, or a combination thereof. Single nucleotide polymorphisms present in target gene sequences include, but are not limited to, 16S rRNA, 23S rRNA, ahpC, alr, embA, embB, embC, ethA, fabG1, folP, gyrA, gyrB, kasA, katG, ndh, parC, parE, pncA, rlmN, rpoB, and/or rpsL genes, RNA molecules derived therefrom, or a combination thereof.
In one aspect, the invention provides a system for practicing the methods of the invention. A method is provided for simultaneously detecting an organism in a sample and its antibiotic resistance comprising the steps: applying a sample comprising a plurality of organisms to the array system; and simultaneously identifying at least one organism in the sample and determining its antibiotic resistance. Probes used in methods and systems of the present invention can be used to detect the presence, absence of at least 44 clinically relevant bacterial species and their associated antibiotic resistance determinants in a single assay. In some embodiments, probes are attached to a substrate. Substrates can comprise any suitable material, including but not limited to glass, plastic, or silicon. Substrates can take any suitable shape, such as a flat surface, a bead, or a microsphere.
In another aspect, an optimized pretreatment process for clinical samples.
The present embodiments are related to system comprising an array and methods for detecting and identifying biomolecules and organisms having antibiotic resistance. More specifically, some embodiments relate to an array system comprising a microarray configured to simultaneously detect a plurality of nosocomial pathogens and clinically relevant antibiotic resistance elements in a sample at a high confidence level.
Before the present invention is further described, it is to be understood that this invention is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges, and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.
It must be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a target locus” includes a plurality of such substrates and reference to “the antibiotic resistance element” includes reference to one or more recombinant polypeptides and equivalents thereof known to those skilled in the art, and so forth. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation.
The term “microarray,” as used herein, refers to an arrangement of distinct polynucleotides arrayed on a substrate, e.g., paper, nylon or any other type of membrane, filter, chip, glass slide, or any other suitable solid support.
As used herein, the term “oligonucleotide” refers to a polynucleotide, usually single stranded, that is either a synthetic polynucleotide or a naturally occurring polynucleotide. The length of an oligonucleotide is generally governed by the particular role thereof, such as, for example, probe, primer and the like. Various techniques can be employed for preparing an oligonucleotide, for instance, biological synthesis or chemical synthesis.
The nucleic acid may be DNA, RNA, or a hybrid and may contain any combination of deoxyribo- and ribo-nucleotides, and any combination of bases, including uracil, adenine, thymine, cytosine, guanine, inosine, xanthanine, hypoxanthanine, isocytosine, isoguanine, and base analogs such as nitropyrrole and nitroindole, etc. Oligonucleotides can be synthesized by standard methods such as those used in commercial automated nucleic acid synthesizers and later attached to an array, bead or other suitable surface. Alternatively, the oligonucleotides can be synthesized directly on the assay surface using photolithographic or other techniques. In some embodiments, linkers are used to attach the oligonucleotides to an array surface or to beads.
As used herein, the term “nucleic acid molecule” or “polynucleotide” refers to a compound or composition that is a polymeric nucleotide or nucleic acid polymer. The nucleic acid molecule may be a natural compound or a synthetic compound. The nucleic acid molecule can have from about 2 to 10,000,000 or more nucleotides. The larger nucleic acid molecules are generally found in the natural state. In an isolated state, the nucleic acid molecule can have about 10 to 50,000 or more nucleotides, usually about 100 to 20,000 nucleotides. It is thus obvious that isolation of a nucleic acid molecule from the natural state often results in fragmentation. It may be useful to fragment longer target nucleic acid molecules, particularly RNA, prior to hybridization to reduce competing intramolecular structures. Fragmentation can be achieved chemically, enzymatically, or mechanically. Typically, when the sample contains DNA, a nuclease such as deoxyribonuclease (DNase) is employed to cleave the phosphodiester linkages. Nucleic acid molecules, and fragments thereof, include, but are not limited to, purified or unpurified forms of DNA (dsDNA and ssDNA) and RNA, including tRNA, mRNA, rRNA, mitochondrial DNA and RNA, chloroplast DNA and RNA, DNA/RNA hybrids, biological material or mixtures thereof, genes, chromosomes, plasmids, cosmids, the genomes of microorganisms, e.g., bacteria, yeasts, phage, chromosomes, viruses, viroids, molds, fungi, or other higher organisms such as plants, fish, birds, animals, humans, and the like. The polynucleotide can be only a minor fraction of a complex mixture such as a biological sample.
The phrases “nucleic acid” or “nucleic acid sequence,” as used herein, refer to a nucleotide, oligonucleotide, polynucleotide, or any fragment thereof. These phrases also refer to DNA or RNA of genomic or synthetic origin which may be single-stranded or double-stranded and may represent the sense or the antisense strand, to peptide nucleic acid (PNA), or to any DNA-like or RNA-like material. In this context, “fragment” often refers to those shorter nucleic acid sequences containing a specific region or loci of interest.
As used herein, the term “hybridize” refers to the process by which single strands of polynucleotides form a double-stranded structure through hydrogen bonding between the constituent bases. The ability of two polynucleotides to hybridize with each other is based on the degree of complementarity of the two polynucleotides, which in turn is based on the fraction of matched complementary nucleotide pairs. The more nucleotides in a given polynucleotide that are complementary to another polynucleotide, the more stringent the conditions can be for hybridization and the more specific will be the binding between the two polynucleotides. Increased stringency may be achieved by elevating the temperature, increasing the ratio of co-solvents, lowering the salt concentration, and combinations thereof.
As used herein, the terms “complementary,” “complement,” and “complementary nucleic acid sequence” refer to the nucleic acid strand that is related to the base sequence in another nucleic acid strand by the Watson-Crick base-pairing rules. In general, two polynucleotides are complementary when one polynucleotide can bind another polynucleotide in an anti-parallel sense wherein the 3′-end of each polynucleotide binds to the 5′-end of the other polynucleotide and each A, T(U), G, and C of one polynucleotide is then aligned with a T(U), A, C, and G, respectively, of the other polynucleotide. Polynucleotides that comprise RNA bases can also include complementary G/U or U/G basepairs. Two complementary strands may comprise complementary regions comprising all or one or more portions of one or both strands.
As used herein, the term “kmer” refers to a polynucleotide of length k. In some embodiments, k is an integer from 1 to 1000. In some embodiments, k is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 125, 150, 175, 200, 250, 300, 400, 500, 600, 700, 800, 900, or 1000.
As used herein, the term “organism” refers to any prokaryote, eukaryote, archaea, fungi or bacteria.
Given the limited microarray real estate, a computational pipeline was developed that would make maximum use of a microarray while still enabling concurrent detection of as many antibiotic resistance elements as possible in a list of our top 24 pathogens (Table 1) or 44 pathogens (Table 4 or Table 7).
In some embodiments, a system of the invention comprises an array targeting the 24 nosocomial pathogens shown here in Table 1. In other embodiments, the array targeting 24 or more pathogens. And in another embodiment, the array targeting 44 or more organisms, the 44 organisms identified in Table 4 or 7 infra.
Acinetobacter baumannii
Bordetella pertussis
Burkholderia cenocepacia
Citrobacter freundii
Clostridium difficile
Enterobacter aerogenes
Enterobacter cloacae
Enterococcus faecalis
Enterococccus faecium
Escherichia coli
Haemophilus influenzae
Klebsiella oxytoca
Klebsiella pneumoniae
Mycobacterium tuberculosis
Neisseria meningitidis
Proteus mirabilis
Pseudomonas aeruginosa
Serratia marcescens
Stenotrophomonas maltophilia
Staphylococcus aureus
Staphylococcus epidermidis
Streptococcus pneumoniae
Streptococcus viridans
Streptococcus pyogenes
The biological mechanisms underlying antibiotic resistance are diverse and complex. Moreover, partly due to varying selective pressures, for specific mechanisms strong biases might exist towards some of these pathogens. An extensive list of genes related to antibiotic resistance was compiled and reviewed.
To represent the most recent sequence information, we mined public sequence databases. Such an approach gives a huge number of sequences. To be useful as a basis for microarray design, the diversity of these sequences was quantified, each sequence annotated, and the sensitivity of different sequence candidates to be put on the microarray was evaluated for sensitivity and specificity.
A schematic or flowchart showing the computational pipeline for the present design of the array is shown in
We initially compiled 22,413 sequences spanning 642 species and 145 antibiotics. Using this sequence set as a “seed”, a total of more than 1 million sequences were harvested from Genbank nr database representing 1392 sequence clusters. Clusters were annotated by antibiotic resistance element, antibiotic resistance mechanism, and host, and cluster sequence representatives were chosen for downstream probe design.
The antibiotic resistance elements clustered generally into the following categories but are not limited to these
The resulting antibiotic resistance element sequences clustered into 1392 clusters according to the various biological mechanisms as detailed in Table 2.
In one embodiment, these seed sequences were used to identify similar sequences found in publicly available databases such as GenBank, and probes were made from those identified sequences. Therefore, in some embodiments, an array system can be fabricated for identification and detection of pathogens listed in Table 1, Table 4 and Table 7 and antibiotic resistance (AR) element sequences shown in Table 5 and listed herein.
Other embodiments provide a method for selecting and/or utilizing a set of oligonucleotide probes for use in an analysis system or bead multiplex system for simultaneously detecting a plurality of organisms in a sample and determining the antibiotic resistance element profile of the organisms in a sample. The method targets known diversity within target nucleic acid molecules to determine if a pathogen or a specific strain is present in the microbial community in the sample and what antibiotic resistance element(s) to which it is associated. In some embodiments, the organism-specific oligonucleotide probes may be used to also establish the antibiotic resistance phenotype. In other embodiments, the array comprises a set of resequencing probes covering antibiotic resistance elements and a set of resequencing probes covering gene(s) that are organism-specific. In some embodiments, this latter set of probes can provide strain-level identification of organisms present in a sample.
Examples of genes for strain-level identification include but are not limited to, 16S rRNA gene, CARDS toxin gene, toxic shock syndrome toxin-1 (tst) gene, adhP gene, adk gene, alpha toxin gene, aroE gene, aspartic semialdehyde dehydrogenase (asd) gene, atl gene, atp operon, cdt (cytolethal distending toxin) toxin gene, cep (cell envelope proteinase) gene, copper resistance (cop) gene, chaperonin cpn60 gene, cyaA gene, eae gene, etk gene, etx gene (epsilon-toxin inducer), folP gene, fumarase (fumC) gene, ferric update regulator (fur) gene, gapdh dehydrogenase gene, gdh dehydrogenase gene, glucose kinase gene, citrate synthase (gltA) gene, gro operon genes, glutamine transport protein (gtr) gene, glycosyltransferase (gttB) gene, IMP dehydrogenase gua gene, DNA gyrases, adhesin gene, gnd gene, groEL gene, hsp65 gene, carboxylesterase (lipT) gene, pepB gene, hsp60 and hsp65 genes, isocitrate dehydrogenase gene, icmB gene, immunity factor for SPN gene, infB gene, katG gene, lepC gene, lgt genes, elt operons, lukPVS and lukPVF genes, mcaP gene, malate dehydrogenase gene, macrophage infectivity potentiator (mip) gene, mitilysin gene, major outer membrane protein (mompS) gene, mismatch repair protein genes, MviN gene, NAD+glycohydrolase (spn) gene, (di)nucleoside polyphosphate hydrolase gene, outer membrane protein II (ompA) gene, catalase-peroxidase (hydroperoxidase I) gene, glucose-6-phosphate isomerase (pgi) gene, pheS gene, plr gene, pneumolysin (ply) gene, pyrazinamidase/nicotinamidas pncA gene, pertactin (prn) gene, zinc metalloproteinase precursor (proA) gene, PtxS1 gene, pyruvate kinase (pykF) gene, recA gene, ribonuclease PH gene, rpoB gene, sctC gene, SCO1/SenC family protein gene, smeZ gene, sodA gene, speA gene, STX transposon-like element and pilus assembly region, tcf gene, tkt gene, tonB-dependent receptor gene, toxA gene, trpA gene, tuf gene, ubiquitous surface protein (usp) gene, or Xanthine phosphoribosyltransferase (xpt) gene.
In another embodiment, the elements whose role in antibiotic resistance are probed are promoter regions of genes. These genes include, but are not limited to, genes such as ethA, embA.
In another embodiment, the antibiotic resistance elements are single nucleotide polymorphisms of specific genes. These genes include, but are not limited to, genes such as 16S rRNA, 23S rRNA, ahpC, alr, embA, embB, embC, ethA, fabG1, folP, gyrA, gyrB, kasA, katG, ndh, parC, parE, pncA, rlmN, rpoB, and rpsL. In some embodiments, target probes directed to detection of these SNPs may be also be designed and provided in addition to the target sequences to detect organisms at the species and/or strain levels.
The oligonucleotide probes can each be from about 5 bp to about 100 bp, preferably from about 10 bp to about 50 bp, more preferably from about 15 bp to about 35 bp, even more preferably from about 20 bp to about 30 bp. In some embodiments, the probes may be 5-mers, 6-mers, 7-mers, 8-mers, 9-mers, 10-mers, 11-mers, 12-mers, 13-mers, 14-mers, 15-mers, 16-mers, 17-mers, 18-mers, 19-mers, 20-mers, 21-mers, 22-mers, 23-mers, 24-mers, 25-mers, 26-mers, 27-mers, 28-mers, 29-mers, 30-mers, 31-mers, 32-mers, 33-mers, 34-mers, 35-mers, 36-mers, 37-mers, 38-mers, 39-mers, 40-mers, 41-mers, 42-mers, 43-mers, 44-mers, 45-mers, 46-mers, 47-mers, 48-mers, 49-mers, 50-mers, 51-mers, 52-mers, 53-mers, 54-mers, 55-mers, 56-mers, 57-mers, 58-mers, 59-mers, 60-mers, 61-mers, 62-mers, 63-mers, 64-mers, 65-mers, 66-mers, 67-mers, 68-mers, 69-mers, 70-mers, 71-mers, 72-mers, 73-mers, 74-mers, 75-mers, 76-mers, 77-mers, 78-mers, 79-mers, 80-mers, 81-mers, 82-mers, 83-mers, 84-mers, 85-mers, 86-mers, 87-mers, 88-mers, 89-mers, 90-mers, 91-mers, 92-mers, 93-mers, 94-mers, 95-mers, 96-mers, 97-mers, 98-mers, 99-mers, 100-mers or combinations thereof.
In some embodiments, the chosen oligonucleotide probes can then be synthesized by any available method in the art. Some examples of suitable methods include printing with fine-pointed pins onto glass slides, photolithography using pre-made masks, photolithography using dynamic micromirror devices, ink jet printing or electrochemistry. In one example, a photolithographic method can be used to directly synthesize the chosen oligonucleotide probes onto a surface. Suitable examples for the surface include glass, plastic, silicon and any other surface available in the art. In certain examples, the oligonucleotide probes can be synthesized on a glass surface at an approximate density of from about 1,000 probes per μm2 to about 100,000 probes per μm2, preferably from about 2000 probes per μm2 to about 50,000 probes per μm2, more preferably from about 5000 probes per μm2 to about 20,000 probes per μm2. In one example, the density of the probes is about 10,000 probes per μm2. The array can then be arranged in any configuration, such as, for example, a square grid of rows and columns. Some areas of the array can be pathogen or organism identification or classification, and others can be used for image orientation, normalization controls or other analyses. In some embodiments, materials for fabricating the array can be obtained from Affymetrix, GE Healthcare (Little Chalfont, Buckinghamshire, United Kingdom), Agilent Technologies (Palo Alto, Calif.), or TessArae (Potomac Falls, Va.).
In one embodiment, the genomic sequence of each antibiotic resistance element is queried by 8, 25-mer i.e. 25 nucleotides in length, probes per base position in the sequence to be detected. For example, if the element is 100 base pairs long and the element is probed with 8 probes per position, then there will be 800 probes to identify that element. Thus, 8 short probes are designed for each base pair in the sequence for each identification or antibiotic resistance element. In certain examples, oligonucleotide fragments are used as probes.
In another embodiment, the presently provided target loci identified may be used for identification and detection of organisms and antibiotic resistance. In some embodiments, short oligonucleotide probes can be designed to cover the entire sequence of each antibiotic resistance element found in the 1392 clusters in Table 2. In such an embodiment, probes can be designed using the target loci sequences of SEQ ID NOS:1-1323 by one having skill in the art.
The target loci are provided herein as SEQ ID NOS: 1-1323, and consist of seed sequences of antibiotic resistance elements (SEQ ID NOS:1-970), organism-specific genes for organism-identification (SEQ ID NOS:971-1232), and regions in genes having antibiotic resistance relevance where a single nucleotide polymorphism is found (SEQ ID NOS:1233-1323).
In some embodiments, oligonucleotide primers can be designed to amplify fragments, specific regions or the entire sequence of each gene or target loci. The primers can be of varying lengths. Primers can be created using the nucleotide sequences of SEQ ID NOS: 1-1323, or surrounding genomic sequence containing and flanking any organism-specific gene or sequence or antibiotic resistance element, for sequence amplification. As is known in the art, primers or oligonucleotides are generally 15-40 bp in length, and usually flank unique sequence that can be amplified by methods such as polymerase chain reaction (PCR) or reverse transcriptase PCR. For all PCR-based methods, primers may be designed using commercially available software, such as OLIGO 4.06 primer analysis software (National Biosciences Inc., Plymouth, Minn.) or another appropriate program, to be, for example, about 19- to 30, or about 22 to 30 nucleotides in length, and in some embodiments, to have a GC content of about 50% or more, and/or to anneal to the template at temperatures of about 68° C. to 72° C.
Methods for design of detector tiles, selection of primers, and configuration of multiplex amplification protocols for the assay are known in the art and also described in U.S. Pat. Nos. 7,979,446; 7,695,941; 7,668,664; and 7,623,997, all of which are hereby incorporated by reference in their entirety.
In one embodiment, the methods for designing suitable probes and methods of fabricating a system herein are as described in International application publication Nos. WO 2010/151842 and in WO 2011/046614, both hereby incorporated by reference in their entireties.
Some embodiments relate to a method of designing or fabricating an array system including identifying antibiotic resistance element sequences corresponding to a plurality of organisms of interest, selecting fragments of antibiotic resistance element and other sequences unique to each organism and creating variant DNA fragments corresponding to the fragments of antibiotic resistance element and, optionally, the sequences unique to each organism and then fabricating the array system.
Non-limiting examples of arrays include microarrays, bead arrays, through-hole arrays, well arrays, and other arrays known in the art suitable for use in hybridizing probes to targets. Arrays can be arranged in any appropriate configuration, such as, for example, a grid of rows and columns. Some areas of an array comprise the detection probes whereas other areas can be used for image orientation, normalization controls, signal scaling, noise reduction processing, or other analyses. Control probes can be placed in any location in the array, including along the perimeter of the array, diagonally across the array, in alternating sections or randomly. In some embodiments, the control probes on the array comprise probe pairs of PM and MM probes. The number of control probes can vary, but typically the number of control probes on the array range from 1 to about 500,000. In some embodiments, at least 10, 100, 500, 1,000, 5,000, 10,000, 25,000, 50,000, 100,000, 250,000 or 500,000 control probes are present. When control probe pairs are used, the probe pairs will range from 1 to about 250,000 pairs. In some embodiments, at least 5, 50, 250, 500, 2,500, 5,000, 12,500, 25,000, 50,000, 125,000 or 250,000 control probe pairs are present. The arrays can have other components besides the probes, such as linkers attaching the probes to a support. In some embodiments, materials for fabricating the array can be obtained from Affymetrix (Santa Clara, Calif.), GE Healthcare (Little Chalfont, Buckinghamshire, United Kingdom) or Agilent Technologies (Palo Alto, Calif.).
In some embodiments, selected oligonucleotide probes are synthesized by any relevant method known in the art. Some examples of suitable methods include printing with fine-pointed pins onto glass slides, photolithography using pre-made masks, photolithography using dynamic micromirror devices, ink jet printing, or electrochemistry. In one example, a photolithographic method can be used to directly synthesize the chosen oligonucleotide probes onto a surface. Suitable examples for the surface include glass, plastic, silicon and any other surface available in the art. In certain examples, the oligonucleotide probes can be synthesized on a glass surface at an approximate density from about 1,000 probes per μm2 to about 100,000 probes per μm2, preferably from about 2000 probes per μm2 to about 50,000 probes per μm2, more preferably from about 5000 probes per μm2 to about 20,000 probes per μm2. In one example, the density of the probes is about 10,000 probes per μm2. The number of probes on the array can be quite large e.g., at least 105, 106, 107, 108 or 109 probes per array.
In one embodiment, the target probes selected and/or utilized by the methodologies of the invention can be organized into tiled sequences that provide an assay with a sensitivity and/or specificity of more than 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%. In some embodiments, sensitivity and specificity depends on the hybridization signal strength, number of probes in the tiled sequence, the number of potential cross hybridization reactions, the signal strength of the mismatch probes, if present, background noise, or combinations thereof. In some embodiments, an AR target sequence containing one probe may provide an assay with a sensitivity and specificity of at least 90%, while another target sequence may require at least 20 probes to provide an assay with sensitivity and specificity of at least 90%.
Besides arrays where probes are attached to the array substrate, numerous other technologies may be employed in the disclosed system for the practice of the methods of the invention. In one embodiment, the probes are attached to beads that are then placed on an array as disclosed by Ng et al. (Ng et al. A spatially addressable bead-based biosensor for simple and rapid DNA detection. Biosensors & Bioelectronics, 23:803-810, 2008).
In another embodiment, probes are attached to beads or microspheres, the hybridization reactions are performed in solution, and then the beads are analyzed by flow cytometry, as exemplified by the Luminex multiplexed assay system. In this analysis system, homogeneous bead subsets, each with beads that are tagged or labeled with a plurality of identical probes, are combined to produce a pooled bead set that is hybridized with a sample and then analyzed in real time with flow cytometry, as disclosed in U.S. Pat. No. 6,524,793. Bead subsets can be distinguished from each other by variations in the tags or labels, e.g., using variability in laser excitable dye content.
In a further embodiment, probes are attached to cylindrical glass microbeads as exemplified by the Illumina Veracode multiplexed assay system. Here, subsets of microbeads embedded with identical digital holographic elements are used to create unique subsets of probe-labeled microbeads. After hybridization, the microbeads are excited by laser light and the microbead code and probe label are read in real time multiplex assay.
In another embodiment, a solution based assay system is employed as exemplified by the NanoString nCounter Analysis System (Geiss G et al. Direct multiplexed measurement of gene expression with color-coded probe pairs. Nature Biotech. 26:317-325, 2008). With this methodology, a sample is mixed with a solution of reporter probes that recognize unique sequences and capture probes that allow the complexes formed between the nucleic acids in the sample and the reporter probes to be immobilized on a solid surface for data collection. Each reporter probe is color-coded and is detected through fluorescence.
In a further embodiment, branched DNA technology, as exemplified by Panomics QuantiGene Plex 2.0 assay system, is used. Branched DNA technology comprises a sandwich nucleic acid hybridization assay for RNA detection and quantification that amplifies the reporter signal rather than the sequence. By measuring the RNA at the sample source, the assay avoids variations or errors inherent to extraction and amplification of target polynucleotides. The QuantiGene Plex technology can be combined with multiplex bead based assay system such as the Luminex system described above to enable simultaneous quantification of multiple RNA targets directly from whole cells or purified RNA preparations.
In one embodiment, the microarray is a resequencing microarray. The resequencing microarray design had two main criteria: (1) to cover the maximum number of sequence variants currently known to be associated with antibiotic resistance and (2) to assure that the chosen sequences are suitable for simultaneous detection of a wide range of genes from multiple organisms and their antimicrobial resistance determinants. In some embodiments, probes are tiled to cover each nucleotide position in every locus to be interrogated, thus enabling not only accurate detection of the selected nosocomial pathogens but also any new variants of these organisms that may emerge.
In some embodiments, the array system uses multiple probes for increasing confidence of identification of a particular organism using an antibiotic resistance gene targeted high density microarray. The use of multiple probes can greatly increase the confidence level of a match to a particular pathogen. Also, in some embodiments, mismatch control probes corresponding to each perfect match probe can be used to further increase confidence of sequence-specific hybridization of a target to a probe. Probes with a mismatch at the 13th nucleotide can be used to indicate non-specific binding and a likely non-match to the sequence of that probe at that nucleotide position.
Arrays and methods of making and using phylogenetic arrays, resequencing arrays and preparing samples are known in the art and are also described in U.S. Pat. Nos. 7,623,997; 7,668,664; 7,961,323; 7,979,446; U.S. Application Publication No. 20070212718 and 20110039710, all of which are hereby incorporated by reference in their entireties for all purposes, and also described in Wang, Z., Daum, L. T., Vora, G. J., Metzgar, D., Walter, E. A., Canas, L. C., Malanoski, A. P., Lin, B. and Stenger, D. A. (2006) Identifying Influenza Viruses with Resequencing Microarrays. Emerg Infect Dis, 12, 638-646; Lin, B., Wang, Z., Vora, G. J., Thornton, J. A., Schnur, J. M., Thach, D. C., Blaney, K. M., Ligler, A. G., Malanoski, A. P., Santiago, J. et al. (2006) Broad-spectrum respiratory tract pathogen identification using resequencing DNA microarrays. Genome Res. 16:527-535, and Davignon, L., Walter, E. A., Mueller, K. M., Barrozo, C. P., Stenger, D. A. and Lin, B. (2005) Use of resequencing oligonucleotide microarrays for identification of Streptococcus pyogenes and associated antibiotic resistance determinants. J Clin Microbiol, 43, 5690-5695; Wilson, W. J., Strout, C. L., DeSantis, T. Z., Stilwell, J. L., Carrano, A. V. and Andersen, G. L. (2002) Sequence-specific identification of 18 pathogenic microorganisms using microarray technology. Mol Cell Probes, 16, 119-127; Wilson, K. H., Wilson, W. J., Radosevich, J. L., DeSantis, T. Z., Viswanathan, V. S., Kuczmarski, T. A. and Andersen, G. L. (2002) High-density microarray of small-subunit ribosomal DNA probes. Appl Environ Microbiol, 68, 2535-2541; Zwick, M. E., McAfee, F., Cutler, D. J., Read, T. D., Ravel, J., Bowman, G. R., Galloway, D. R. and Mateczun, A. (2005) Microarray-based resequencing of multiple Bacillus anthracis isolates. Genome Biol, 6, R10; Wong, C. W., Albert, T. J., Vega, V. B., Norton, J. E., Cutler, D. J., Richmond, T. A., Stanton, L. W., Liu, E. T. and Miller, L. D. (2004) Tracking the evolution of the SARS coronavirus using high-throughput, high-density resequencing arrays. Genome Res, 14, 398-405; Sulaiman, I. M., Liu, X., Frace, M., Sulaiman, N., Olsen-Rasmussen, M., Neuhaus, E., Rota, P. A. and Wohlhueter, R. M. (2006) Evaluation of affymetrix severe acute respiratory syndrome resequencing GeneChips in characterization of the genomes of two strains of coronavirus infecting humans. Appl Environ Microbiol, 72, 207-211; and Hacia, J. G. (1999) Resequencing and mutational analysis using oligonucleotide microarrays. Nat Genet, 21, 42-47, all of which are hereby incorporated by reference for all purposes.
As used herein, a “sample” is from any source, including, but not limited to a biological sample, a gas sample, a fluid sample, a solid sample, or any mixture thereof.
Other methods of sample processing and handling to extract DNA from a sample are known in the art. See Nylund L, Heilig H G, Salminen S, de Vos W M, Satokari R, “Semi-automated extraction of microbial DNA from feces for qPCR and phylogenetic microarray analysis”, J Microbiol Methods. 2010 November; 83(2):231-5. Epub 2010 Sep. 16; Yu and Morrison, Improved extraction of PCR-quality community DNA from digesta and fecal samples, Biotechniques 2004 May; 36(5):808-12; Verollet R, A major step towards efficient sample preparation with bead-beating, Biotechniques. 2008 May; 44(6):832-3, all of which are hereby incorporated by reference in their entirety.
In one embodiment, a novel culture-independent resequencing microarray diagnostic and methods capable of strain-level identification across a panel of clinically-relevant nosocomial pathogens and also supporting prediction of their antibiotic resistance phenotype. In some embodiments, the diagnostic and methods can provide strain-level identification within 48, 24, 18, 12, or 8 hours. In one embodiment, the diagnostic and methods provide strain-level-identification in 8 hours.
Another advantage of the present embodiments is that simultaneous detection of a majority of currently known top pathogens and the type of antibiotic resistance element is possible with one sample. While achieving the results from each of these tests in parallel, the present resequencing microarray system should prove to be more cost effective, provide faster results, and greater sensitivity. This allows for much more efficient study and determination of particular organisms within a particular sample. Current microarrays do not have this capability.
In some embodiments, the samples used can be environmental samples from any environmental source, for example, naturally occurring or artificial atmosphere, water systems, soil or any other sample of interest. In some embodiments, the samples may be obtained from, for example, atmospheric pathogen collection systems, manufacturing plants involved in food preparation or handling, hospital or clinic exam rooms and surfaces, etc. In a preferred embodiment, the array system of the present embodiments can be used in any environment.
In other embodiments, the sample used with the array system can be any kind of clinical or medical sample. In one embodiment, the clinical sample comprises at least one of tissue, skin, stool, bodily fluid, or blood. Tissues can include biopsied cells from various organs or systems including but not limited to, lungs, throat, esophagus, stomach, intestinal, bone, spinal, brain, skin, etc. For example, samples from blood, the lungs or the gastrointestinal tract of mammals may be assayed using the array system. Also, the array system of the present embodiments can be used to identify an infection in the blood of an animal. The array system of the present embodiments can also be used to assay medical samples that are directly or indirectly exposed to the outside of the body, such as the lungs, ear, nose, throat, the entirety of the digestive system or the skin of a patient or an animal.
More specifically, the DNA (also referred to as “nucleic acid”) for use in the present invention may be obtained by collecting a biological sample from a patient and subsequently directly applying the sample to further microarray analysis or extracting (i.e., isolating or substantially purifying) the DNA from the sample for further analysis. In this regard, the biological sample includes, but are not limited to, peripheral blood; exfoliated cells, including cells obtained from a buccal swab, stool, sputum, nasal wash, nasal aspirate, nasal swab, throat swab, bronchial lavage, vaginal swab, and rectal swab; blood, blood cells (e.g., white cells), tissue or fine needle biopsy samples, urine, peritoneal fluid, visceral fluid, and pleural fluid, or cells therefrom.
Further, the present invention is not limited to biological samples obtained from humans. The present invention may also be applied to biological samples obtained from any animal species including domestic and/or farm animals including, but not limited to: dogs, cats, horses, cows, pigs, goats, sheep, rabbits, mice, rats, etc. In addition, the present invention may also be applied to biological samples obtained from any animal species that may be found in the wild or traditionally thought of as zoological animals, for example: monkeys, giraffes, elephants, zebras, tigers, lions, lemurs, etc. Further, the present invention may also be applied to biological samples obtained from any avian species. In this embodiment it is understood that the gene targets embedded on the microarray chip to be detected would contain the genes for the respective species selected.
Further, the sample of the present invention is not limited to biological samples, the sample of the present invention may be environmental (air, water, soil, etc.), animal (see above), or plant (e.g., cells obtained from any portion of a plant where the species of plant is without limit). Again, in this embodiment it is understood that the gene targets embedded on the microarray chip to be detected would contain the genes for the respective species selected, when that species is known (i.e., animal or plant). Further, when the sample is environmental, the gene targets embedded on the microarray chip can be any predetermined collection that is used to detect and identify any pathogen or organism of interest, for example.
In some embodiments, the sample is a processed or unprocessed food product. In other aspects, the food sample comprises at least one of meat, turkey, chicken and other poultry, milk, eggs, eggs products, dairy products, fresh or dried fruits and vegetables and their juices, grains, fish, seafood, pet food, baby food and infant formula.
In another embodiment, the sample is a bacterial isolate, to confirm or identify the strain and its antibacterial resistance profile.
It is anticipated that the organism-specific and antibiotic resistance (AR) probes in an array system can be used as a clinical diagnostics tool in hospitals, to aid in epidemiological research and tracking as well as for infection control. In addition, current methodology can be applied to redesign a new microarray containing different antibiotic resistance genes and organisms geared towards other uses. These would include but not limited to biodefense, product and food safety and assessment of air, soil and water quality.
Some embodiments relate to methods of detecting an organism in a sample using a resequencing array system. These methods include contacting a sample with one organism or a plurality of organisms to the array system of the present embodiments and detecting the organism or organisms. In some embodiments, the organism or organisms to be detected are bacteria. In some embodiments, the antibiotic resistance elements detected represent new or emerging resistance in the organism or organisms detected in the sample.
Sample processing for Affymetrix platform microarrays has already been extensively validated, however as one of the primary goals is to produce a rapid diagnostic tool, optimization for time to result will require some re-focusing of existing protocols. Affymetrix microarrays are now being used in clinical laboratories, demonstrating their potential as a rapid diagnostic. In one embodiment, a processing method combining an automated robotic DNA/RNA extraction system with a streamlined resequencing microarray protocol to rapidly provide high quality material for analysis allowing for high sensitivity, accuracy and reproducibility in detecting and profiling antibiotic resistance phenotypes of select nosocomial pathogens. In another embodiment, a random DNA amplification approach may be used to provide the sensitivity necessary to be comparable with current clinical culture methods.
In one embodiment, the assay for clinical sample processing including a pre-treatment process comprising longer periods of bead beating to increase the amount of DNA extracted. Typically 30 s of bead beating are used to extract DNA, however periods of 45 s, 60 s, 90 s and 120 s of bead beating was found to be effective in increasing the amount of DNA extracted particularly in samples of Gram positive organisms, without sacrificing the integrity of DNA extracted from Gram negative species in the same sample. This approach has been compared to enzymatic lysis methods and found to be more rapid and efficacious in retrieval of nucleic acids from samples.
In another embodiment, a protein such as bovine serum albumin (BSA) is added to the sample (e.g., extracted nucleic acid sample) to decrease PCR inhibition in blood samples and further enhance the sensitivity of detection. In some embodiments, the protein is added to the sample prior to extended bead beating period. In one embodiment, the protein is added in amounts of 80 to 100 CFU per mL of sample.
In another embodiment, the pre-treatment method further comprising cell lysis methods using enzymatic lysis of bacterial cells, such as in the case of Gram positive organisms that are difficult to lyse due to a thick peptidoglycan cell wall. Enzymes such as lysostaphin may be added to the clinical sample and processed.
Thus, in some embodiments, an assay and methods for clinical sample processing is described. Such a method comprising steps of (1) collecting a sample from a patient; (2) adding sample to beads; (3) performing bead beating of said sample for 45 to 120 seconds to extract DNA from the sample and (4) adding 80 to 100 U mL−1 of bovine serum albumin to the PCR reaction with nucleic acids from said sample as DNA template.
In some embodiments, identification of organisms will define antibiotic treatment regime. For example if a Gram-positive organism is determined to the primary pathogen, the patient would receive a gram-positive appropriate antibiotic such as vancomycin. In addition, if the assay determines that a specific organism is present that possesses resistance determinants for a number of antibiotics, these therapeutic options would be avoided for that particular patient.
Depending on the culture source, organism, and clinical microbiology laboratory practices, final identification and susceptibility results are usually not available for 48 to 72 hours; for some organisms (for example, fungi or Mycobacteria), susceptibility testing may take weeks or may never be available. This delay creates a window during which patients are exposed to the toxicity and selective pressure of unnecessary broad-spectrum antimicrobial therapy. Indeed, for less-severe infections there is the potential that final microbiology results will not be available before the patient is discharged, and the information may never be used to modify antimicrobial therapy. Thus the present invention further provides for a rapid detection and antibiotic susceptibility testing method to substantially reduce the lag time to appropriate antimicrobial therapy from days to hours, thus optimizing patient outcomes and preventing the development and dissemination of antibiotic-resistant organisms.
Standard methods for drug susceptibility testing can fail to identify the presence of important mechanisms of resistance that are associated with clinical failure, despite apparent phenotypic susceptibility. Examples of this phenomenon include extended-spectrum beta-lactamase production in Klebsiella species, ribosomal methylation in Staphylococci and Streptococci, and heterogenous vancomycin resistance in Staphylococci (See Lewis J S, 2nd, Jorgensen J H. Inducible clindamycin resistance in Staphylococci: should clinicians and microbiologists be concerned? Clin Infect Dis 2005; 40:280-5; Paterson D L, Ko W C, Von Gottberg A et al. Outcome of cephalosporin treatment for serious infections due to apparently susceptible organisms producing extended-spectrum beta-lactamases: implications for the clinical microbiology laboratory. J Clin Microbiol 2001; 39:2206-12; Liu C, Chambers H F. Staphylococcus aureus with heterogeneous resistance to vancomycin: epidemiology, clinical significance, and critical assessment of diagnostic methods. Antimicrob Agents Chemother 2003; 47:3040-5). In these cases, standard microbroth-based susceptibility techniques must be supplemented by additional phenotypic tests, further delaying the provision of important susceptibility data to the clinician. Rapid identification of organisms harboring these resistance characteristics could reduce the risk of application of inappropriate therapies.
Strain-specific virulence factors, such as those responsible for toxin production or biofilm formation, are increasingly recognized as potentially important contributors to clinical outcomes in infected patients. Recognition of strains possessing these factors has the potential to alter management through more aggressive surgical intervention, removal of prosthetic material (such as intravascular catheters), and use of agents targeting protein synthesis to prevent toxin production. There is growing interest in the development of pharmaceutical agents that block or modulate virulence factors (Marra A. Targeting virulence for antibacterial chemotherapy: identifying and characterising virulence factors for lead discovery. Drugs R D 2006; 7:1-16). However, current routine clinical microbiology laboratory techniques are insufficient to identify organisms possessing these factors. For example, a new strain of the intestinal pathogen Clostridium difficile producing a novel toxin and with an expanded antimicrobial resistance profile has emerged as a cause of severe colitis (McDonald L C, Killgore G E, Thompson A et al. An epidemic, toxin gene-variant strain of Clostridium difficile. N Engl J Med 2005; 353:2433-41; Loo V G, Poirier L, Miller M A et al. A predominantly clonal multi-institutional outbreak of Clostridium difficile-associated diarrhea with high morbidity and mortality. N Engl J Med 2005; 353:2442-9). Critically, this new strain co-exists with previous, less pathogenic strains making diagnosis more difficult. For example, using the presently described system and methods for identification of patients carrying this new strain could lead to a lower threshold for surgical intervention and more intensive and focused antimicrobial therapy.
Finally, routine clinical microbiologic laboratory techniques provided do not allow infection-control practitioners to identify relatedness of isolates from different patients. Isolate relatedness is useful in determining if an outbreak is occurring and in pinpointing its source. Current methods, using pulsed field gel electrophoresis are time consuming and do not typically provide meaningful results until after the outbreak has occurred. In some embodiments, the present invention provides for the ability to identify markers allowing strain differentiation of infecting pathogens in the course of routine microbiological workup and represent an extremely useful advance in technology from an infection-control standpoint.
Other applications of the presently described system and array is the monitoring of organisms and antibiotic resistant bacteria in food and beverage production, animal husbandry, water supplies, treated human waste that may be applied to agricultural land, etc.
Other applications of the presently described system and array is the monitoring of organisms modified for biological warfare.
To date, we have collected at least 20 representative strains for 22 of 44 pathogenic bacterial species (Table 1, 3), generating a bank of 604 clinical isolates of which 567 strains are characterized with respect to their antibiotic resistance phenotype (determined by standard clinical laboratory techniques appropriate for that strain and antibiotic-susceptibility profile). On-going work includes characterization, in our CLIA-approved laboratory of the resistance profile of Haemophilus influenzae which is not routinely profiled for antibiotic resistance in the clinical lab. All strains have been successfully cultured under species-specific optimal culture conditions (aerobic and anaerobic). Stock cultures have been made, banked and cataloged for every strain and parallel DNA and RNA extractions have been performed for every strain, quantified, cataloged and stored at −80° C. We are currently a BSL II approved laboratory and as such are not permitted to work with viable cells of BSL III pathogens such as Neisseria meningitis and Mycobacterium tuberculosis. To ensure that we had representative strains of these species for array validation and model building, we obtained pathogen-free nucleic acid extracts from Drs. Joanna MacKichan (Environmental Science and Research, New Zealand) and Midori Kato-Maeda (San Francisco General Hospital). In addition, due to the limited species banked at the clinical laboratory at UCSF, we obtained additional strains of specific organisms from investigators who specifically study these species, including Drs. John LiPuma (Burkholderia cepacia), Tim Murphy (H. influenzae) and the California State Reference laboratory (Bordatella pertussis). A database, which we generated, has been populated with unique identifiers, antibiotic resistance phenotype and source of isolate (if available). This extensive collection of characterized strains (Table 3) will be made available to other researchers at the end of the study.
P. aeruginosa
E. coli
K. pneumonaie
K. oxytoca
E. cloacae
E. aerogenes
A. baumanii
S. marcescens
S. maltophilia
C. freundii
B. cepacia
P. mirabilis
H. influenzae
S. aureus
S. epidermidis
S. pneumonaie
S. viridans
E. faecium
E. faecalis
N. meningitides*
C. difficile**
M. tuberculosis*
The UCSF Clinical Microbiology Lab is in the process of collecting 80 clinical stool samples from patients with suspected Clostridium difficile-associated diarrhea. Nucleic acids will be extracted and used to determine C. difficile genotype at the loci chosen for the array-based assay, as well as validate the sensitivity and specificity of the oligonucleotide probes tiling this region on the array. With the addition of these stool samples, we will have a collection of DNA and RNA from 684 strains and samples, with parallel clinically determined, antibiotic resistance data. All data on these strains/extracts, nucleic acid concentration extracted, antibiotic phenotype has been inputted into a searchable database.
We have commenced genotyping of these strains using bi-directional Sanger sequencing of the 16S rRNA gene from each isolate. 16S rRNA gene sequencing has been performed for every strain in our collection. Contiguous sequences spanning the length of the entire 16S rRNA gene (˜1.5 Kb) have been generated for each strain and searched against existing publically available databases to determine the identity of each strain. We have performed agreement statistics on the data generated and demonstrated that of the 11 species and 380 strains genotyped to date, the kappa score is 0.87 with a statistically significance value of p<0.001. Comparative analysis of these sequences at the species level has demonstrated that the lack of agreement is primarily restricted to a small number of species, where clinical identification appears to be relatively inaccurate e.g. Enterobacter cloacae.
On-going work involves performing similar genotypic analysis on the target loci and whole genome sequencing of strains with poor representation in publically available databases prior to their use to validate the prototype resequencing array-based assay to complement the large phenotypic database of information we have generated for these strains.
We continue to enroll patients in our sepsis study and in our intravenous drug users with suspected endocarditis and to store blood collected from consented subjects in these studies for validation of the resequencing array-based assay. In addition we have collected and banked more than 300 cystic fibrosis sputum samples that will also be used to validate the assay. Through one of our other NIH-funded airway microbiome studies, we are also collecting HIV positive airway samples from San Francisco General Hospital, and Mulago Hospital in Kampala (high rate of Mycobacterium tuberculosis infection). A subset of these bronchoalveolar lavage samples that have been clinically examined by culture-based methods and by culture-independent approaches will also be used to validate the resequencing array-based assay.
Building on our method for sample collection, handling and storage, we have continued to examine aspects of this protocol that may impact efficiency of the extraction protocol and, consequently the ability of the resequencing array-based assay to detect and profile strains. Further optimization of bacterial DNA extraction, yield, and PCR-based quantification from blood samples is being pursued. We have found that longer periods of bead beating increases the amount of DNA extracted by the Qiagen BioRobot method (an automated system for rapid extraction of nucleic acids from samples) particularly that of gram positive organisms, without sacrificing the integrity of DNA extracted from Gram negative species in the same sample (dark gray bars,
As described above, we compiled a comprehensive and solid set of antibiotic resistance elements and their associated annotations. Of the actual sequences tiled as detectors throughout the RPM-BAR 1.5 designed array, there are 3 classes: antibiotic resistance (AR) gene targets (SEQ ID NOS: 1-970), Organism/species identification (BUG-ID) gene targets (SEQ ID NOS: 971-1232), and SNP targets (SEQ ID NOS: 1233-1323) selected genes known to be associated with bacterial antibiotic resistance bearing mutations in those genes that are deemed determinants of resistance.
The AR-genes are consensus sequences of clusters of sequence-similar antibiotic resistance genes. The target loci in each of the sequence records was from a manually curated set and seeded from the University of Maryland ARDB (database of sequence records for AR genes) to identify in excess of 1 million sequence-similar sequence records from the entire GenBank. This large aggregate of sequence records was condensed first to about 16,000 consensus sequences of aligned records, using a constraint of approximately 98% sequence similarity, and another constraint that each cluster contain at least one record attributing its origin from one of the 22 target bacterial species.
The 16,000 clusters were further merged to about 1,600 by sequence alignments using less stringent constraint of 95% sequence similarity, and then purged of clusters representing a single outlier sequence, or of length less than about 400 bp. The length limit was to ensure that detector tiles of 200 to 224 bp length could be identified from each cluster's consensus sequence, leaving enough flanking sequences to the detector tile for selection of multiplex amplification primers.
The BUG-ID gene targets are selected genes for RPM array-based detection and identification of selected species. An initial list of targeted bacterial genera (genuses) was selected based on ongoing objectives and clinical requirements of the overall project.
The subset of GenBank sequence records attributed to the previously-selected target genera was surveyed. This extended to multiple species per genus, and extended to other genera from other TessArae RPM applications that were suggested to be candidates for inclusion in the RPM-BAR 1.5 assay.
We selected the final list of genera and species to be targeted in the assay and designed detector tiles of 224 bp lengths, following established assay design protocols. In general, alignments of sequence records for each target genus and for such genes represented in the database (GenBank) were aligned, and multiple gene targets were selected to represent multiple strains and variants of the target genus/species. In most cases the targeted genes represented housekeeping functions, not necessarily linked to antibacterial resistance mechanisms. When large numbers of different strains and variants contributed to a target organism gene cluster, multiple detector tiles were selected from sub-cohorts of sequence records based on sequence record similarity.
The SNP targets represent selected genes known to be associated with bacterial antibiotic resistance bearing mutations in those genes that are deemed determinants of resistance.
We then conducted: a thorough literature search which provided citations of particular mutations in particular genes of particular species, and these were aggregated to define regions of the target genes that could be targeted sequences of the application.
Following selection of target sequences, we then selected intervals spanning proximal mutations as re-sequencing detector tiles of variable lengths, for the purpose of evaluating sequences of targeted bacterial genes in selected specimens for determination of bacterial genotype (mutations known and previously unknown).
We have also created a prototype database of antibiotic resistance elements named BARChipDB. BARChipDB will be used to store three types of information: (1) annotated sequence clusters represented on the array, (2) related sequence clusters harvested from GenBank, and (3) clinical isolate metadata (antibiotic resistance phenotype, clinical source, geographic origin etc.). BARChipDB is implemented as a PostgreSQL relational database. The generic model organism database (GMOD) schema Chado was chosen to store sequence and annotations of the ˜16,000 sequence clusters. The main advantage of Chado is that it is driven by ontologies, which makes it highly flexible and generic. In addition, Chado SQL API has a library of SQL functions for efficiently performing useful operations on biological data. We are in the process of designing a second customized schema expanding Chado to organize the available experimental and in silico analyses data. We envision that BARChipDB will be instrumental in handling continuous updates of antibiotic resistance sequence diversity from GenBank, streamlining future assay updates, and facilitating array-based assay output interpretation.
We completed tiling probe sets for all candidate detector tiles, apportioned to Bacterial genera/species (262 tiles) and Resistance determinants (1030). The array platform we are using has the capacity to accommodate 1,345 tiles of up to 224 bp each, we therefore dramatically expanded the targets included on the array from 11 to 44 clinically relevant bacterial species and their associated antibiotic resistance determinants and are currently at 99.96% of the array capacity. These additional species were chosen based on their clear role in pathogenesis and their detection in a number of recent airway microbiome studies. The final list of all bacterial species to be detected by this tool are described in Table 4 or Table 7. These targets are represented by 262 tiles totaling 58,688 bp (of a possible 303,000 bp) on the array. The 262 tiled sequences are identified herein as SEQ ID NOs: 971-1232. The probes for each tile are the same as the sequence for each tile/target plus the complement of that sequence and 3 mismatch probes for each perfect match. Each base across that tile is covered by 8 probes on the resequencing array.
Acinetobacter baumannii
Burkholderia ambifaria
Burkholderia cenocepacia
Burkholderia cepacia
Burkholderia dolosa
Burkholderia multivorans
Burkholderia pyrrocinia
Burkholderia stabilis
Burkholderia
vietnamiensis
Bordetella parapertussis
Bordetella pertussis
Clostridium difficile
Citrobacter freundii
Chlamydophila
pneumoniae
Chlamydia trachomatis
Enterobacter aerogenes
Enterobacter cloacae
Enterococcus faecalis
Enterococcus faecium
Escherichia coli
Haemophilus influenzae
Haemophilus
parainfluenzae
Klebsiella oxytoca
Klebsiella pneumoniae
Legionella pneumophila
Mycobacterium avium
hominissuis
Mycobacterium avium
paratuberculosis
Mycobacterium kansasii
Mycobacterium
tuberculosis
Moraxella catarrhalis
Mycoplasma pneumoniae
Neisseria meningitidis
Pseudomonas aeruginosa
Pseudomonas
pseudoalcaligenes
Proteus mirabilis
Proteus vulgaris
Staphylococcus aureus
Stenotrophomonas
maltophilia
Serratia marcescens
Streptococcus mitis
Streptococcus mutans
Streptococcus
pneumoniae
Streptococcus pyogenes
Streptococcus viridans
Resistance determinants are split into two categories—genes in which SNP accumulation leads to antibiotic resistance and genes for which their presence in the genome alone confers a resistance phenotype. Although the resequencing array will, by the nature of the data it generates (actual nucleotide sequence), will report novel SNPs detected in any target, those genes specifically linked to SNP-associated resistance targeted by the array-based assay are listed in Table 3. These targets are represented by 198 tiles, totaling 58,568 bp on the array. The regions of the targets are identified as SEQ ID NOS: 1233-1323.
Bacterial species known to house these antibiotic resistance genes and resistance-associated SNPs that are targeted by the resequencing array-based assay are listed in Table 6.
Acinetobacter
baumannii
Bordetella pertussis
Burkholderia cepacia
Citrobacter freundii
Clostridium difficile
Enterobacter aerogenes
Enterobacter cloacae
Enterococcus faecalis
Enterococcus faecium
Escherichia coli
Haemophilus influenzae
Klebsiella oxytoca
Klebsiella pneumoniae
Mycobacterium tuberculosis
Neisseria meningitidis
Proteus mirabilis
Pseudomonas aeruginosa
Serratia marcescens
Staphylococcus aureus
Stenotrophomonas maltophilia
Streptococcus pneumoniae
Streptococcus pyogenes
Finally, the remaining antibiotic resistance targets represent all other antibiotic resistance determinants and are covered on the array by 832 consensus sequencing tiles totaling 217,280 bp. In summary the novel resequencing array content includes detection of 44 clinically relevant bacterial species, 21 target genes with documented SNP-associated resistance and 16,000 clusters of antibiotic resistance determinants whose presence is associated with resistance to clinically relevant antimicrobial agents.
This system has major implications for early detection and antibiotic profiling of nosocomial pathogens. Several studies have demonstrated that early and appropriate antimicrobial administration significantly increases patient survival rates, and decreases length of hospital stay and associated health-care costs. This diagnostic, and particularly the expanded and more comprehensive array-based assay we are developing, will significantly decrease the time taken to diagnose patients.
Resequencing Array Fabrication.
We have fabricated a 49-format Affymetrix Custom Resequencing microarrays capable of sequencing a total of 350 kb. Each nucleotide base across the chosen loci (typically 224 bases) will be interrogated using four 25 mer probes for each strand differing only at the central 13th nucleotide position where each of the four base possibilities (A, T, G, C) is represented. As validated for other Affymetrix microarrays, the probe that perfectly matches the base at that position in the target will have a significantly greater hybridization intensity thus producing a base call at the position. Not only will this enable detection of previously characterized strains and resistance genotypes but may also allow new variants to be detected. We believe this additional aspect will prove highly valuable in epidemiological studies where novel strains or novel antibiotic resistance variants may be detected.
A sample assay protocol that may be used is similar to most other nucleic acid-based protocols, and contains several standard procedures. Beginning with a clinical or environmental specimen, the steps are: (a) Extraction of total nucleic acids (TNA) using one of several commercially available methods; (b) Reverse Transcription to convert any RNA to cDNA using random primers; (c) PCR endpoint amplification of pathogen-specific gene sequences using locus-specific, multiplexed primers; (d) Sample pooling and purification combines the multiplex PCR reactions, removes any residual primers, enzymes, salts, dNTPs, and concentrates the amplified DNA; (e) Fragmentation and labeling prepares the amplified targets to be hybridized to the microarray; (f) Hybridization, staining and washing allows for the detection of the target sequences on the microarray; (g) Internal Controls monitor the efficiency of amplification and hybridization steps.
An optimized assay protocol should combine the following:
Nucleic Acid Extraction Optimization.
Further optimization of bacterial DNA extraction, yield, and PCR-based quantification from blood samples is being pursued. We have found that longer periods of bead beating increases the amount of DNA extracted by the BioRobot method, particularly that of Gram positive organisms, without sacrificing the integrity of DNA extracted from Gram negative species in the same sample (orange bars,
Target Amplification Optimization.
We will test random multiple displacement amplification (MDA) of bacterial DNA following subtraction of human DNA to determine the suitability of this target amplification method. This will be compared with a multi-locus PCR approach. Using the data obtained from our comparative genomics, we performed an initial demonstration of multiple pathogen detection capability. We developed the Multi-Pathogen Identification (MPID) microarray capable of detecting eighteen pathogenic viruses, prokaryotes, and eukaryotes, including several CDC Category A and B biothreat agents. Pathogens targeted are shown in Table 1 and Table 7.
Reduction and Optimization of Array Processing Time.
We will reduce the minimum times for template fragmentation, labeling, and hybridization and also the minimum times for array washing, staining and scanning so that the entire array process takes only 6 hours from receipt of template.
Analysis.
Both the resequencing and gene expression arrays are run on the GCS 3000 instrumentation system, Cartridge-based instrument system used in microarray applications. Standard cartridge-based array processing involves hybridization to an array, washing and staining, and scanning step. Analysis of array hybridization patterns will be used to generate a sequence readout of each locus according to an approach previously published by us (Metzgar D, Myers C A, Russell K L, Faix D, Blair P J, Brown J, Vo S, Swayne D E, Thomas C, Stenger D A, Lin B, Malanoski A P, Wang Z, Blaney K M, Long N C, Schnur J M, Saad M D, Borsuk L A, Lichanska A M, Lorence M C, Weslowski B, Schafer K O, Tibbetts C. Single assay for simultaneous detection and differential identification of human and avian influenza virus types, subtypes, and emergent variants. PLoS One. 2010 Feb. 3; 5 (2):e8995. PubMed PMID:20140251; PubMed Central PMCID: PMC2815781.). Each assay of a specimen generates sequence data as base calls (A, G, C, or T) across each detector tile of Affymetrix CustomSeq-formatted microarrays (see Affymetrix Technical Note, 2006, GeneChip CustomSeq Resequencing Array Base Calling Algorithm Version 2.0: Performance in Homozygous and Heterozygous SNP Detection). Image data acquired from GeneChip Instrument System scanning under GeneChip Operating Software control is translated by GSEQ sequence analysis software (Affymetrix Inc., Santa Clara, Calif.). TessArray Sequence Analysis (TSEQ) software evaluates a “C3 Score” for each array detector tile, as a metric of detected DNA sequence quantity and quality. The C3 Score is the total number of GSEQ-identified nucleotides that appear in runs of three or more consecutive (non-N) base calls, expressed as percentage of the length (nucleotides) of each array detector tile sequence. This approach to definition of a detected sequence reduces background noise from spurious false-positive hybridizations of 25-base oligonucleotide probes that could lead to isolated and relatively uninformative single base calls. Relaxed and stringent target organism detection and reporting thresholds for the assay can been statistically and empirically established for all of the resequencing detector tiles. All sequences from an assay that meet a detection and reporting threshold are automatically subjected to alignment-based search of the BARChipDB Reference Sequence Database, using a dedicated server-based implementation of the Basic Local Alignment Search Tool, BLAST.
Final confidence in identification of an organism species/strain or resistance element will comprise of a single ‘score’ reflecting a combination of probability scores from the BLAST scores of independent loci for each strain/resistant element.
We are currently validating primer pairs which will be used in multiplex PCR reactions to amplify the target loci of interest. We confirm that each primer pair for identification of a specific species is capable of amplifying the target from DNA extracted from a known strain of that species (strain identification has been confirmed by sequence analysis). In the same manner, primer pairs to amplify specific target loci aimed at determining the presence or SNP content of specific antibiotic resistance determinants will be validated using strains known to encode those resistance determinants. We will perform the initial validation of the resequencing microarray made in Example 2 in two phases. First we will assay representative cultures of the pathogenic bacteria that have complete or near complete genome sequences available. Knowing the exact genetic composition of the strains applied will provide the most confidence in predicting hybridization and base-calling patterns during the optimization phase. Then we will apply all sequenced strains in a Latin Square type study to determine detection sensitivity and base-call accuracy under polymicrobial conditions in the absence of human DNA.
Following this we will assay spiked blood or stool samples containing either genome sequenced representatives or clinical isolates whose antibiotic resistance phenotype has previously been characterized. This will provide detection specificity and sensitivity data in the presence of any potential background interference from clinical samples. Target interference will be detected by comparing probe-set response to the organism from pure-culture (II-B: Pure genomes) versus mixed genomes (II-B: Latin Square assay) or spiked clinical material (II-B: Clinical spike-ins). All probes affected by interference will be removed from the final probe sets.
Pure Genomes:
DNA will be extracted from representative bacterial strains with fully sequenced genomes and hybridized to the microarray. Where available we will initially assess locus quality and sequence base-call accuracy using two sequenced representative strains of each target species. Only a single concentration of template DNA will be tested at this point. This will allow initial evaluation of base-call accuracy and locus response in a well-characterized genetic background. Each locus will pass QC if 99% of the base calls from PM probes match the expected gene sequences and are differentiated from the 3 mM probes with quality score thresholds of at least 12 (i.e. the maximum for homozygous data). For this test with sequenced genomes in a non-complex background, if the array-derived sequence diverges from the database sequence due to ambiguous base-calls at non-SNP positions the probe set will be retained but truncated to remove dependence upon ambiguous positions.
Latin Square Assay:
We will perform a latin square type hybridization study by spiking in genomic DNA from each of the bacterial species using DNA from genome sequenced representatives (where available) or well characterized clinical isolates in some cases. In this assay DNA from each species is added to the hybridization in rotating concentrations such that the total DNA quantity on each array is the same. Using for example 10 arrays each organism will be assayed at 10 different concentrations in a complex background together with the other bacteria. This represents a polymicrobial infection scenario and will allow us to determine the limits of detection and interference (e.g. probe cross-hybridization) in such cases. At this point we will also assay pure cultures of a defined number of selected clinical isolates with defined antibiotic resistance phenotypes from each species to determine accuracy in phenotype prediction. The concentration of DNA to be used for this assay will be based upon the results of the latin square assay described above.
Clinical Spike-Ins:
The final step in determining detection sensitivity, base-call accuracy and locus reliability is to spike known concentrations of bacteria into clinical samples (sterile blood for most, stool for C. difficile). In this assay we will use one sequenced bacterium (where available) and one clinical isolate for each species to be tested. These intact organisms will be spiked into sterile blood or C. difficile negative stool samples at four concentrations in duplicate.
Nucleic Extraction Optimization.
Extractions using the Qiagen BioRobot EZ1 will be as sensitive and accurate as current “research lab” methods and will show reduced intra-sample variability. Nucleic acid extraction efficiency and integrity will be optimized using the automated EZ1 robotic system (Qiagen, CA). A modified protocol of the Qiagen All Prep DNA/RNA extraction kit we have developed in our lab will be used in parallel to compare nucleic acid extraction efficiency of both methods.
Pure Bacterial Cultures.
Pure cultures of clinical isolates of each of the 10 test organisms will be grown overnight prior to serial dilution in sterile PBS. One ml volumes of varying culture dilutions (in the range 10−1-10−9) will be extracted by both EZ1 (Qiagen, CA) automated and a manual modified All Prep (Qiagen, CA) method (see protocol below) to determine the extraction efficiencies of each method. One hundred μl volumes of each dilution will also be plated in triplicate on LB agar plates, or appropriate agar e.g. blood or chocolate agar for specific organisms and incubated aerobically or anaerobically (i.e. C. difficile) at 37° C. overnight to enumerate bacterial CFUs so that extraction efficiency can directly be related to bacterial cell counts
Spiked Blood Samples.
Following assessment of each method for extraction of nucleic acids from pure culture, spiked-in experiments will be carried out as described above with the exception that in each case 1 ml dilutions of cultures will centrifuged and resuspended in a small volume (50 μl of sterile PBS) prior to addition to 950 μl of blood and subsequent extraction and CFU count determinations. This will evaluate extraction efficiency in the presence of blood components. One hundred microliters volumes of each sample will be plated in triplicate on appropriate agar plates and incubated at 37° C. overnight to enumerate bacterial CFUs so that extraction efficiency in the presence of clinically relevant fluids (i.e. components of blood) can be assessed. PCR inhibition is a well-documented problem when extracting from blood collected in blood-culture bottles. This is generally attributed to sodium polyethanol sulfate (86) and/or to haemoglobin and lactoferrin (87). To eliminate this potential problem, blood samples will be collected using PreAnalytiX PAXgene Blood DNA and RNA tubes. Blood samples are drawn directly into evacuated PAXgene Blood Tubes via standard phlebotomy technique. Tubes are sterile and contain additives that stabilize nucleic acids for subsequent purification. For long-term storage, samples will be stored at −80° C. PCR poison assays will be carried out using low concentrations of spiked bacterial DNA into blood extracts to test for PCR inhibition.
Clinical Blood Samples.
Following optimization of the extraction method, 10 ml clinical blood samples taken from septic patients will be used for extraction. Bacterial quantitative cultures will be carried out on the same blood samples. This will permit a direct comparison between the results of clinical culture and our extraction and detection method to be made
We will reduce the minimum times for template fragmentation, labeling, and hybridization and also the minimum times for array washing, staining and scanning so that the entire array process takes only 6 hours from receipt of template. Currently, the standard resequencing protocol can take 3 days to complete. Template DNA extraction, amplification, quantification and concentration normalization can be accomplished on the first day. Fragmentation, labeling of the fragmented DNA and hybridization to the arrays is carried out on the second day, followed by washing and staining and then scanning of the arrays on the third day. The current standard protocol calls for an overnight hybridization of 16 hours for the array. Successful resequencing of microbial targets has been accomplished with this method (Lin B, Wang Z, Vora G J et al. Broad-spectrum respiratory tract pathogen identification using resequencing DNA microarrays. Genome Res 2006; 16:527-35, Davignon L, Walter E A, Mueller K M et al. Use of resequencing oligonucleotide microarrays for identification of Streptococcus pyogenes and associated antibiotic resistance determinants. J Clin Microbiol 2005; 43:5690-5, Wang Z, Daum L T, Vora G J et al. Identifying influenza viruses with resequencing microarrays. Emerg Infect Dis 2006; 12:638-46). However, other reports using targets found in high abundance in the microbial cell, e.g. 16S and 23S genes, have used shorter hybridization times of an hour or less at higher temperatures (Troesch A, Nguyen H, Miyada C G et al. Mycobacterium species identification and rifampin resistance testing with high-density DNA probe arrays. J Clin Microbiol 1999; 37:49-55, Couzinet S, Jay C, Barras C et al. High-density DNA probe arrays for identification of staphylococci to the species level. J Microbiol Methods 2005; 61:201-8, Gonzalez R, Masquelier B, Fleury H et al. Detection of human immunodeficiency virus type 1 antiretroviral resistance mutations by high-density DNA probe arrays. J Clin Microbiol 2004; 42:2907-12).
The acceptability of using a standard volume of amplified template without concentration normalization will be determined based on the reproducibility of the accuracy of the sequencing calls over a range of starting template concentrations. This will result in a saving of both time and the need for associated laboratory equipment.
The fragmentation and labeling steps of the protocol are enzymatic reactions that have been optimized for human genomic DNA templates. The concentration of the fragmentation reagent and terminal deoxynucleotidyl transferase will be optimized to enable shorter reaction times than the current 30 minutes and 2 hours respectively. The new conditions will be tested over a broad range of input concentrations to ensure that the signal to noise ratio on the arrays is not adversely affected.
The relationship between the hybridization time and temperature will be investigated with all targets present on the array and optimized for improved signal to noise ratios to produce high quality sequencing calls. The effect of known DNA hybridization enhancers, e.g. single stranded binding protein, on the hybridization time to produce acceptable signal intensity will also be investigated. These factors will be optimized using amplified material from negative samples spiked with either high or low genome copies of the target organisms. The final outcome of this optimization will be a hybridization time of less than three hours producing high quality sequence data.
The final diagnostic will comprise of an optimized protocol in which, for example, blood, will be collected in a Paxgene tube, which we have determined results in maintenance of sample integrity and is most amenable to downstream molecular assays. Collected samples will be subjected to our optimized nucleic acid extraction protocol which includes increased periods of bead-beating (45 s-120 s) and followed by automated extraction using the Qiagen Biorobot. Following this, multi-plex amplification reactions will be performed with the addition of BSA to improve amplification efficiency and diminish amplification inhibitory effects. Amplified products will be fragmented, labeled with biotin and applied to the microarray. Optimization of hybridization conditions to minimize time while maximizing sensitivity and specificity is on-going. Finally data is fed through the TessArae analysis pipeline (Potomac Falls, Va.) to provide an interpretable data report for each sample.
Nucleic extraction methods to be used represent one or more approaches based on our prior publications (Roediger, F. C., Slusher, N. A., Cox, M. J., Pletcher, S. D., Goldberg, A. N. and Lynch, S. V. Optimizing Bacterial DNA Extraction from Maxillary Sinus Samples. Am. J. Rhinol Allergy. 2010 July; 24(4):263-5. PMID: 20819463; Huang, Y. J., Nelson, C. E., Brodie, E. L., DeSantis, T. Z., Baek, M. S., Liu, J., Woyke, T., Allgaier, M., Bristow, J., Wiener-Kronish, J. P., Sutherland, R., King, T. S., Icitovic, N., Martin, R. J., Asthma Clinical Research Network Investigators, Boushey, H. A., and Lynch, S. V. Airway Microbiota and Bronchial Hyperresponsiveness in Patients with Sub-optimally Controlled Asthma. J. Allergy Clin. Immunol. J Allergy Clin Immunol. 2011 February; 127(2):372-381.e1-3. Epub 2010 Dec. 30. PMID: 21194740; Cox, M. J., Allgaier, M., Taylor, B., Baek, M. S., Huang, Y. J., Daly, R. A., Karaoz, U., Andersen, G. L., Brown, R., Fujimura, K. E., Wu, B., Tran, D., Kofff, J., Kleinhenz, M. E., Nielson, D., Brodie, E. L. and Lynch, S. V. Airway Microbiota and Pathogen Abundance in Age-Stratified Cystic Fibrosis Patients. (PLoS One PLoS One. 2010 Jun. 23; 5(6):e11044). PMID: 20585638; Cox, M., Huang, Y. J., Fujimura, K., Liu, J., McKean, M., Brodie, E. L., Boushey, H., Cabana, M. and Lynch, S. V. Lactobacillus casei Abundance is Associated with Profound Shifts in the Infant Gut Microbiome. PLoS One. 2010 Jan. 18; 5(1); Ivanov, LI., Atarashi, K., Manel, N., Brodie, E. L., Shima, T., Karaoz, U. Wei, D., Goldfarb, K. C., Santee, C. A., Lynch, S. V., Imaoka, A. Itoh, K., Takeda, K., Umesaki, Y., Honda, K., and Littman, D. R. Cell. 2009 Oct. 30; 139(3):485-98.
As described above, we compiled a comprehensive and solid set of antibiotic resistance elements and their associated annotations. Of the actual sequences tiled as detectors throughout the designed array, there are 3 classes: antibiotic resistance (AR) gene targets (SEQ ID NOS: 1-970), Organism/species identification (BUG-ID) gene targets (SEQ ID NOS: 971-1232), and SNP targets (SEQ ID NOS: 1233-1323) selected genes known to be associated with bacterial antibiotic resistance bearing mutations in those genes that are deemed determinants of resistance.
The same methods as described in Example 1 were used to curate the sequences and select the target sequences.
We completed tiling probe sets for all candidate detector tiles, apportioned to Bacterial genera/species (262 tiles) and Resistance determinants (1061). The array platform we are using has the capacity to accommodate 1,345 tiles of up to 224 bp each, we therefore dramatically expanded the targets included on the array from 11 to 44 clinically relevant bacterial species and their associated antibiotic resistance determinants and are currently at 99.96% of the array capacity. These additional species were chosen based on their clear role in pathogenesis and their detection in a number of recent airway microbiome studies. The final list of all bacterial species to be detected by this tool are described in Table 7. These targets are represented by 262 tiles totaling 58,688 bp (of a possible 303,000 bp) on the array. The probes for each tile are the same as the sequence for each tile/target plus the complement of that sequence and 3 mismatch probes for each perfect match. Each base across that tile is covered by 8 probes on the resequencing array.
Acinetobacter baumannii
Burkholderia ambifaria
Burkholderia cenocepacia
Burkholderia cepacia
Burkholderia dolosa
Burkholderia multivorans
Bordetella parapertussis
Bordetella pertussis
Burkholderia pyrrocinia
Burkholderia stabilis
Burkholderia vietnamiensis
Clostridium difficile
Citrobacter freundii
Chlamydophila pneumoniae
Chlamydia trachomatis
Enterobacter aerogenes
Enterobacter cloacae
Escherichia coli
Enterococcus faecalis
Enterococcus faecium
Haemophilus influenzae
Haemophilus parainfluenzae
Klebsiella oxytoca
Klebsiella pneumoniae
Legionella pneumophilia
Mycobacterium avium
Moraxella catarrhalis
Mycobacterium kansaii
Mycoplasma pneumoniae
Mycobacterium tuberculosis
Neisseria meningitidis
Pseudomonas aeruginosa
Proteus mirabilis
Pseudomonas pseudoalcaligenes
Proteus vulgaris
Staphylococcus aureus
Staphylococcus epidermidis
Stenotrophomonas maltophilia
Serratia marcescens
Streptococcus mitis
Streptococcus mutans
Streptococcus pneumoniae
Streptococcus pyogenes
Streptococcus viridans
Genes specifically linked to SNP-associated resistance targeted by the array-based assay are listed in Table 7 above. These targets are represented by 91 tiles, totaling 58,568 bp on the array. The regions of the targets are identified as SEQ ID NOS: 1233-1323.
Finally, the remaining antibiotic resistance targets represent all other antibiotic resistance determinants and are covered on the array by 970 consensus sequencing tiles totaling 217,280 bp. In summary the novel resequencing array content includes detection of 44 clinically relevant bacterial species, 21 target genes with documented SNP-associated resistance and 16,000 clusters of antibiotic resistance determinants whose presence is associated with resistance to clinically relevant antimicrobial agents.
This resequencing array can be fabricated and used in applications as described above.
It will be appreciated, however, that the present embodiments may be practiced in many ways and should be construed in accordance with the appended claims and any equivalents thereof. Any patents, publications or references cited herein are hereby incorporated by reference in their entireties for all purposes.
This application is a non-provisional continuation-in-part application of and claims priority to PCT/US2011/048698 filed on Aug. 22, 2011, and to U.S. Provisional Patent Application No. 61/375,816 filed on Aug. 21, 2010, both of which are herein incorporated by reference in their entirety.
This invention was made with Government support under Contract No. DE-AC03-05CH11231 awarded by the Department of Energy and under Grant No. U01 AI075410-01 awarded by the NIH/NIAID. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61375816 | Aug 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2011/048698 | Aug 2011 | US |
| Child | 13773631 | US |
