Patent Application
20170191054
The present invention relates generally to compositions and methods useful for the extraction of biological materials, such as nucleic acids, proteins and other biological molecules from biological samples. More specifically, the present invention relates to the separation and purification of nucleic acids and proteins from biological samples.
In the following discussion certain articles and methods will be described for background and introductory purposes. Nothing contained herein is to be construed as an “admission” of prior art. Applicants expressly reserve the right to demonstrate, where appropriate, that the articles and methods referenced herein do not constitute prior art under the applicable statutory provisions.
In diagnostic and biochemical methodologies, access to extracted or purified cellular components, such as nucleic acids, and access to extracted or purified forms of proteins is imperative. Access to nucleic acids is required in such methodologies as nucleic acid sequencing, direct detection of particular nucleic acid sequences by nucleic acid hybridization and nucleic acid sequence amplification techniques. Therefore, a method for extracting and purifying nucleic acids should be simple, rapid and require little, if any, additional sample manipulation to gain the desired access to the nucleic acid. A method with all of these features would be extremely attractive in the automation of sample preparation, a goal of research and diagnostic laboratories. Access to purified forms of proteins is achieved through such techniques as exclusion chromatography, ion exchange chromatography, differential precipitation and the like. These methodologies, however, are troublesome for various reasons. For example, precipitation techniques are still crude and difficult to automate, and often result in unacceptable loss of sample, while chromatography is expensive and time consuming.
Effective methods for purification and manipulation of nucleic acids using paramagnetic particles are disclosed in U.S. Pat. No. 5,973,138 (“138”) and U.S. Pat. No. 6,433,160 (“160”), each incorporated herein by reference in their entirety. The paramagnetic particles used therein, reversibly bind to nucleic acids in the biological samples and allow for separation of the nucleic acids from some of the other components in the biological samples. Once separated, the bound nucleic acids are removed from the paramagnetic particles via an elution/neutralization buffer. The paramagnetic particles are then removed from the elution/neutralization buffer containing the nucleic acids. The buffer containing the nucleic acids may be used in further manipulation of the separated nucleic acids, such as hybridization, restriction, labeling, reverse transcription and amplification.
Protein purification by rapid fractionation from crude biological samples is disclosed in U.S. Pre-Grant Publication 2006-0030056 (“0056”), herein incorporated by reference in its entirety. Proteins in biological samples are separated by reversibly binding a protein molecule in a biological sample to a paramagnetic particle. The sample may be further processed to obtain a protein sample in a more pure form or a sample depleted of select proteins. A method that would increase the separation and isolation of components or biological samples, such as nucleic acids and proteins, from the sample would improve the product available for diagnostic and biochemical methodologies.
The present invention is directed to a method of extraction and purification of components of biological samples. Accordingly, one aspect of certain embodiments of the present invention is to provide methods useful for the extraction of nucleic acids, proteins and other biological molecules from biological samples.
Another aspect of certain embodiments of the present invention is to provide a method for extracting and purifying components of biological samples that is simple, rapid and requires little, if any, additional sample manipulation.
A further aspect of certain embodiments of the present invention is to provide a method that would increase the efficiency of separation and isolation of components of a biological sample.
Another aspect of certain embodiments of the present invention is to provide improved processes for optimizing extraction of components of biological samples. These optimized extraction processes significantly increase the capability of separating and recovering components, such as nucleic acids and purified protein, for further diagnostic and biochemical methodologies.
Another aspect of certain embodiments of the present invention is to provide a method of extracting and purifying components of biological samples with a two-step elution and neutralization process that improves the capability for separation and recovery of the components.
Embodiments of the present invention provide a method of extracting and purifying components from biological samples using pH adjustment of buffers for elution and neutralization of target biological components.
Embodiments of the present invention also include kits for carrying out the method of extraction and purification of components of a biological sample, such as biological molecules, organelles, and cells from biological samples.
The present invention is directed generally to methods for extraction and purification of components of biological samples. The present invention describes a method of extracting a nucleic acid from a biological sample, wherein the extracted nucleic acid may be further manipulated by such means as hybridization, restriction, labeling, reverse transcription and amplification methodologies. Furthermore, the present invention describes a method of separating and purifying protein from a biological sample. The methods described herein present improved processes for optimizing extraction of nucleic acids, proteins and other biological molecules from biological samples. These optimized extraction processes significantly increase the separation and recovery of nucleic acids, purified protein, and other biological molecules for further diagnostic and biochemical methodologies.
As used herein, the terms “purifying” and “purification” also include extracting/extraction, isolating/isolation and concentrating/concentration and do not require absolute purity, but instead only require removal of some of or all of at least one of the components of the biological sample. In practice it is presumed that practitioners will purify to about 80% or more, preferably 80%, 90%, 95% or greater purity.
The biological samples used according to the present invention, for example, clinical, forensic or environmental samples, may be any biological material, preferably containing nucleic acid. These samples may contain any viral or cellular material, including prokaryotic and eukaryotic cells, viruses, bacteriophages, mycoplasms, protoplasts and organelles, or any parts thereof. A component of a biological sample as used herein may be any part of the sample, including biological material and biological molecule(s). Such biological materials may comprise all types of mammalian and non-mammalian animal cells, plant cells, algae (including blue-green algae), fungi, bacteria, yeast, protozoa and viruses. Embodiments of this invention can be used to extract biological molecules, such as nucleic acids, proteins, carbohydrates, organelles, cells, or portions of these compositions. Representative examples of biological materials include blood and blood-derived products such as whole blood, plasma and serum; clinical specimens such as semen, urine, feces, sputa, tissues, cell cultures and cell suspensions, nasopharangeal aspirates and swabs, including endocervical, vaginal, occular, throat and buccal swabs; and other biological materials such as finger and toe nails, skin, hair, and cerebrospinal fluid or other body fluid. Environmental samples include soil, water, air, suspension effluents, powders and other sources of nucleic acid containing material.
The biological samples of the present invention may be pretreated to ensure release of nucleic acids into the biological sample for extraction. The pretreatment of biological samples for this purpose are described in U.S. Pre-Grant Publication 2004-0157218 (“'7218”), incorporated herein by reference in its entirety. As disclosed in '7218, a protein denaturant may preferably be used in the pretreatment process. A protein denaturant that is useful in the present invention includes an agent(s) that causes an increase in pH, such as potassium hydroxide (KOH).
The nucleic acids of the present invention are preferably reversibly bound to paramagnetic particles as disclosed by the methods of '138 and '160. In '138 and '160, it was found that when in an acidic environment, the paramagnetic particles of the invention will reversibly bind nucleic acid molecules without the necessity of an anionic detergent as taught in International Publication No. WO 96/18731. As used herein, the term paramagnetic particle(s) means particle(s) as described in '138 and '160.
Within the meaning of the present invention, the method steps for separation of the paramagnetic particle-bound nucleic acids from other biological sample components are preferably those method steps disclosed in '138 and '160.
In a preferred embodiment, the paramagnetic particle-bound nucleic acid molecules may be eluted with an appropriate elution buffer accomplished by raising the pH of such environment. In previous methods, the elution step comprised the addition of a buffer designed in general to remove the nucleic acids from the paramagnetic particles and to neutralize the solution at the same time for further manipulation, such as hybridization, restriction, labeling, reverse transcription and amplification. Removing the nucleic acids from the paramagnetic particles in a separate step from neutralization allows optimization of the elution buffer pH for the removal of the nucleic acid, thereby unexpectedly achieving an increased capability to separate and recover unbound nucleic acid relative to that achieved with the previous one-step elution/neutralization type buffers. As described herein, paramagnetic particles, such as iron oxide, bind negatively charged nucleic acids at acidic pH with a net positive charge. At neutral to basic pH, the paramagnetic particles, such as iron oxide, are no longer positively charged and release the nucleic acids. Agents which can be used to aid the elution of nucleic acid from paramagnetic particles include, but are not limited to, basic solutions such as potassium hydroxide (KOH), sodium hydroxide (NaOH) or any compound which will increase the pH of the environment to an extent sufficient that electronegative nucleic acid is displaced from the paramagnetic particles.
The condition for elution of nucleic acid occurs at pH values at about 8 to 14. Elution at the highest possible pH without degradation is desired to prevent non-specific self-annealing of the nucleic acid strand and to optimize release of the nucleic acids from the paramagnetic particles. Elution at high pH and denaturation of DNA:DNA, DNA:RNA or RNA:RNA hybrids is also beneficial for downstream applications that require single-stranded target, such as hybridization, in particular probe hybridization, or amplification, in particular isothermal nucleic acid amplification. Maintenance of the target nucleic acid in a single-stranded form precludes the need for subsequent heat denaturation prior to hybridization of complementary primers or probes. Self-annealing could promote entanglement of the nucleic acid with the paramagnetic particle itself and prevent separation of the nucleic acid from the paramagnetic particle at the elution step. Other particle types could use the concept of elution followed by neutralization.
The particle-bound nucleic acids are eluted with the elution buffer until the desired result is achieved. For example, the nucleic acids may be eluted from the paramagnetic particles with the addition of an elution buffer composed of KOH and mixing, for example by aspirating and dispensing a given volume, until the desired result is achieved. While this method is successful for separation of DNA and RNA, care should be taken to avoid pH values and/or exposure times that might lead to degradation of nucleic acid.
By removing the bound nucleic acids in this manner, the pH is optimized to achieve the maximum release of bound nucleic acids. Surprisingly, it was found that by performing the elution step separately and allowing for the use of higher pH values resulted in an increased reproducibility of signal generation in downstream nucleic acid amplification assays relative to that achieved using a combined elution/neutralization buffer. The improved capability to recover and/or detect the nucleic acids was unexpected. Therefore, separating the elution step from the neutralization step provides a significant advantage over the previous approaches.
In a preferred embodiment, a neutralization buffer may be added after the elution step. The neutralization buffer adjusts the pH value of the elution solution containing the unbound nucleic acids to a preferred pH range of about 6 to about 9, depending on the downstream application, more preferably about 8 to about 8.5, and most preferable about 8.4. By neutralizing the solution containing the unbound nucleic acids in this manner, the pH environment is optimized for further nucleic acid manipulation, such as hybridization, restriction, labeling, reverse transcription and amplification. This may be achieved by using any neutralization buffer suitable for achieving the optimized pH value for further manipulation. A preferred neutralizing buffer is bicine, as is used in the examples below. Alternative neutralization buffers include but are not limited to Tris, CUES [2-(cyclohexylamino)ethanesulfonic acid], BES [N-N-Bis(2-hydroxyethyl)-2-aminoethanesulfonic acid], MOPS (4-morpholinepropanesulfonic acid) and phosphate. Other neutralizing buffers useful in the method of the present invention can be readily ascertained by one of skill in the art using routine screening methods that do not require undue experimentation.
After neutralization of the sample, the paramagnetic particles are removed while the pH optimized solution containing the unbound nucleic acids is transferred for further manipulation, such as hybridization, restriction, labeling, reverse transcription and amplification for example. Magnetic force is preferably used to separate the paramagnetic particles, as described herein.
In a preferred embodiment of the present invention, proteins can be extracted from a biological sample for purification. Extraction is preferably achieved by reversibly binding at least one protein in the biological sample to at least one paramagnetic particle, as described herein. Once bound, the particle-protein complex is preferably separated from unbound components of a biological sample, preferably achieved by use of magnetic forces applied to the sample. The sample containing the particle-protein complex is then washed and then separated from the wash. The protein is then removed from the paramagnetic particle by eluting the sample with an optimized basic pH elution buffer yielding an eluted sample. This allows for optimized recovery of proteins from the paramagnetic particle. Once the protein is eluted from the paramagnetic particle, a neutralizing buffer is added with the paramagnetic particles then being separated from the elution/neutralization buffer mixture. Removal of the neutralized paramagnetic particles preferably can be achieved through magnetic forces applied to the neutralized buffer sample. Once the paramagnetic particles are separated from the neutralization buffer containing the unbound proteins, the proteins can be further utilized in diagnostic and biochemical methodologies. The significance of the present invention is the increased recovery of unbound proteins by the separation of the elution/neutralization step used in previous methods.
Yet another aspect of the present invention is to provide kits for treating a biological sample for the extraction of biological materials there from. The kits may comprise at least one protein denaturant as described herein. The kits may contain water and buffer solutions as described herein, as well as paramagnetic particles or other solid supports for extraction and/or purification, which are described in more detail elsewhere. The kits may also contain one or more of the following items for processing and assaying the biological samples: collection devices such as swabs, tubes and pipettes; controls; pH indicators; and thermometers. Kits may include containers of reagents mixed together in suitable proportions for performing the method in accordance with the present invention. Reagent containers preferably contain reagents in unit quantities that obviate measuring steps when performing the subject method. Kits of the present invention may include optimized elution buffers for releasing nucleic acids from paramagnetic particles, as described herein. Kits may include neutralizing buffers for optimizing downstream applications, such as nucleic acid hybridization, restriction, labeling, reverse transcription and amplification, as described herein.
The kits of the present invention may also include the reaction mixtures, as well as methods of extracting nucleic acid from the reaction mixtures. The reaction mixtures may comprise at least one protein denaturant for particular embodiments as needed. The reaction mixtures may in some embodiments include various reagents used with the subject reaction mixtures to purify and detect nucleic acids, such as buffers and iron oxide or other solid supports for nucleic acid purification.
The invention will now be described in greater detail by way of the specific examples. The following examples are offered for illustrative purposes and are not intended to limit the invention in any manner. As would be apparent to skilled artisans, various changes and modifications are possible and are contemplated within the scope of the invention described. The following examples illustrate the effectiveness of the compositions and methods of the present invention to pretreat whole blood and plasma samples for optimized nucleic acid extraction and optimized manipulation. Whole blood and plasma are among the most challenging samples for nucleic acid extraction because of their highly proteinaceous content; therefore, the methods of the present invention are expected to be effective for other biological samples as well. In these examples, the reversible binding of nucleic acid molecules on paramagnetic particles in an acidic environment is used for nucleic acid isolation from the reaction mixture resulting from treating samples for extraction of intact nucleic acid according to the present invention. The binding pH is preferably about 1 to about 6.5, more preferably about 1 to about 4, and most preferably about 2. The elution pH is preferably about 8 to about 14. Once of skill in the art will appreciate that the elution pH is preferably optimized by using a pH that is as high as possible without causing degradation of the nucleic acids of the sample. The paramagnetic particle technology captures nucleic acids non-specifically, or independent of sequence. After neutralization, the pH is preferably about 6.0-9.0 depending on the downstream application. More preferably the pH is about 8 to about 8.5, and most preferably about 8.4.
This example was performed to determine if treatment of the samples with 150 mM KOH elutes DNA from the iron oxide better than heat alone.
The materials used in this example were as follows:
Plasma was prepared from whole blood by spinning whole blood in Plasma Pretreatment Tubes (PPT) at 1,100 g for 10 minutes. A 6 ml volume of pooled plasma was prepared. Ten thousand Chlamydia trachomatis (CT) Elementary bodies (EB) were added per milliliter to the plasma pool, which was dispensed in equal volumes into six 2 ml centrifuge tubes. Another 10 ml bacterial suspension was prepared in deionized water with 10,000 CT EB/ml and dispensed in 10×1 ml volumes. A further suspension was prepared containing 10,000 CT EB/ml in 300 mM Bicine-containing 2× sample buffer.
Forty milligrams of iron oxide were dispensed into four of the tubes of plasma; 80 ul of acetic acid was dispensed into two of the tubes, and 300 ul of acetic acid were added to two tubes containing plasma but no iron oxide. All six of the tubes were placed into a lysolyzer for 30 minutes at 105° C. Forty milligrams of iron oxide were added to the two tubes containing no iron oxide following lysolyzation; 80 ul of acetic acid were added to the two tubes containing no acid. After mixing, recovery of the iron oxide and removal of the specimen matrix, the particles were washed two times with 1 ml/tube of deionized water. One tube of each condition was treated with 500 ul of 150 mM KOH for 15 minutes prior to addition of 300 mM Bicine 2× sample buffer. As controls, one tube from each condition had 75 mM KOH/150 mM Bicine-containing 2× sample buffer added.
Forty milligrams of iron oxide were spiked into two of the 10 tubes with 10,000 CT EB/ml in deionized water. Two tubes containing no iron oxide had 80 ul of acetic acid added and two tubes containing iron oxide had 300 ul of acetic acid added. These tubes and four tubes with no prior acid treatment were lysolyzed at 105° C. for 30 minutes. The tubes containing iron oxide prior to lysis had 80 ul dispensed into each. The remaining tubes had 40 mg of iron oxide added and all the tubes were placed on an end-over-end rocker for 30 minutes. After recovery of the iron oxide, the particles were washed two times with 1 ml/tube of deionized water. One tube from each condition was treated with 500 ul of 150 mM KOH for 15 minutes prior to addition of 300 mM Bicine 2× sample buffer. As controls, one tube of each type had 75 mM KOH/150 mM Bicine 2× sample buffer added.
The eluates from all the tubes were boiled for 5 minutes and the lysates were tested using microwells from the BD ProbeTec™ Chlamydia trachomatis Amplified DNA Assay (Little et al., Clin Chem 1999; 45:777-784).
The MOTA (Metric Other Than Acceleration) value represents the area under the curve of relative fluorescence over time. The established cutoff for a positive reaction with the CT assay is 2,000 MOTA. It is evident that, in the majority of cases, higher MOTA scores were obtained from lysates exposed to the two-step elution process (KOH followed by neutralization with Bicine).
This example demonstrates recovery of RNA using a two-step elution process.
The materials used in this example were as follows:
Plasma was pretreated with 44% formamide and 5U Proteinase K for 20 minutes at 65 C and 10 minutes at 70 C. Iron oxide and 180 ul of binding acid were added to the plasma. The mixtures were then spiked at 10,000 copies/ml of HIV gag gene transcript. After binding to the ferric oxide and washing, the RNA was eluted with 120 ul of either 80 mM or 100 mM KOH elution buffer for 20 minutes at 65 C. The remaining elutate was neutralized with 60 ul of either 192 mM or 230 mM bicine and mixed for 2 minutes. The RNA was reverse transcribed with AMV-RT and amplified by SDA using gag-specific primers. (Nycz et al., Anal Biochem, 1998; 259:226-234). Detection occurred in real time using a fluorescent detector probe. (Nadeau et al., Anal Biochem, 1999; 276:177-187).
The samples for which the lower 80 mM KOH concentration was used for elution produced higher MOTA values, indicating more robust amplification/detection of target RNA. It is likely that exposure to the higher concentration of KOH (100 mM) caused hydrolysis and degradation of the RNA transcripts. This experiment therefore demonstrates the ability of ferric oxide extraction with the two step elution process to recover RNA from a complex biological matrix. Unexpectedly, exposure of RNA to a high pH during the elution step did not cause degradation of the target nucleic acid.
The example was performed to determine if heat during elution at different KOH concentrations affects the stability and/or recovery and/amplification/detection of RNA.
The materials used in this example were as follows:
Plasma was pretreated with 44% formamide and 5U Proteinase K for 20 minutes at 65 C and 10 minutes at 70 C. Iron oxide and 180 ul of binding acid were added to the plasma. The mixtures were then spiked at 5,000 copies of HIV gag gene transcript/ml. After binding to the ferric oxide and washing, the RNA was eluted with 120 ul of either 60 mM, 70 mM or 80 mM KOH elution buffer for either 2 minutes without heat or for 20 minutes at 65 C. The samples were neutralized immediately by mixing with 60 ul of 230 mM bicine for 2 minutes. The RNA was reverse transcribed with AMV-RT and amplified by SDA using gag-specific primers. (Nycz et al., Anal Biochem, 1998; 259:226-234). Detection occurred in real time using a fluorescent detector probe. (Nadeau et al., Anal Biochem, 1999; 276:177-187).
Positive MOTA values (>2000) were obtained under all conditions. These data, therefore, indicate that it may be possible to elute RNA from ferric oxide without employing heat using a two-step elution method involving exposure to KOH followed by neutralization with bicine. The procedure without heat has the advantage of requiring less sophisticated instrumentation.
This experiment was performed to optimize elution conditions.
The materials used in this example were as follows:
Plasma was pretreated with 44% formamide and 5U Proteinase K for 20 minutes at 65 C and 10 minutes at 70 C. Iron oxide and 180 ul of binding acid were added to the plasma. The mixtures were then spiked at 10,000 copies of HIV gag gene transcript/ml. After binding to the ferric oxide and washing, the RNA was eluted with 120 ul of either 46 mM, 55 mM, 63 mM or 80 mM KOH elution buffer for 20 minutes at 65 C. The samples were then neutralized with 60 ul of 109 mM bicine and mixed for 2 minutes. The RNA was reverse transcribed with AMV-RT and amplified by SDA using gag-specific primers. (Nycz et al., Anal Biochem, 1998; 259:226-234). Detection occurred in real time using a fluorescent detector probe. (Nadeau et al., Anal Biochem, 1999; 276:177-187).
RNA was successfully recovered from plasma using the two step elution procedure. These data show, however, that higher MOTA values were obtained when the RNA was eluted in the presence of heat, irrespective of the buffer conditions employed for amplification/detection.
The example evaluated smaller elution volume with the two-step elution process.
The materials used in this example were as follows:
Plasma was pretreated with 44% formamide and 5U Proteinase K for 20 minutes at 65 C and 10 minutes at 70 C. Iron oxide and 180 ul of binding acid were added to the plasma. The mixtures were then spiked at 10,000 copies of HIV gag gene transcript/ml. After binding to the ferric oxide and washing, the RNA was eluted with 120 ul of either 50 mM, 65 mM, and 80 mM KOH for 20 minutes at 65 C. The samples were then neutralized with 60 ul of either 154 mM, 192 mM or 230 mM bicine and mixed for two minutes. The RNA was reverse transcribed with AMV-RT and amplified by SDA using gag-specific primers. (Nycz et al., Anal Biochem; 1998; 259:226-234). Detection occurred in real time using a fluorescent detector probe. (Nadeau et al., Anal Biochem, 1999; 276:177-187).
Robust amplification of the RNA target was achieved under each of the conditions tested, as determined by the high MOTA scores. These data demonstrate the utility of iron oxide extraction followed by a two-step elution process for the recovery of amplifiable RNA from a complex biological matrix. No RNA hydrolysis was evident from exposure to different concentrations of KOH for 20 min at 65 C.
This example details the separation of elution and neutralization steps compared to one-step method and the effect on MOTA.
The materials used in this example were as follows:
Plasma was pretreated with 44% formamide and 5U Proteinase K for 20 minutes at 65 C and 10 minutes at 70 C. Iron oxide and 180 ul of binding acid were added to the plasma. The mixtures were then spiked at 10,000 copies of HIV gag gene transcript/ml. After binding to the ferric oxide and washing, the RNA was eluted with 400 ul of either 50 mM, 65 mM or 80 mM KOH elution buffer for 20 minutes at 65 C. The eluates were split into volumes of 100 ul and 300 ul, each of which was neutralized with a different bicine-containing neutralization buffer (Table 6). The RNA was reverse transcribed with AMV-RT and amplified by SDA using gag-specific primers. (Nycz et al, Anal Biochem, 1998; 259:226-234). Detection occurred in real time using a fluorescent detector probe. (Nadeau et al., Anal Biochem, 1999; 276:177-187).
MOTA scores improved with decreased KOH concentration during elution, suggesting that the RNA target might be partially degraded by prolonged exposure to strong alkali. Elution with lower concentration KOH improved MOTA scores indicating more robust amplification/detection.
The purpose of this experiment was to determine the elution efficiency of DNA from ferric oxide using the BD Viper™ System in extracted mode. This study was designed to evaluate whether there was amplifiable target DNA still bound to the iron oxide after the final elution step in the ferric oxide extraction process when conducted using an SDA compatible buffer (approximately pH 8.4). In a previous experiment it was determined that if ferric oxide is re-exposed to elution buffer of this pH and the second eluate tested in an SDA reaction positive fluorescent signals will result. One of the possible reasons for this was to the presence of trace quantities of elution buffer after the original extraction. To mitigate this potential, all extraction tubes in this experiment had the remaining elution buffer form the initial extraction event removed prior to re-elution with additional SDA compatible buffer. This was accomplished by washing the ferric oxide with deionized water (pH 4-5) to prevent further elution of any bound DNA. No clinical matrix was used in this experiment.
The materials used in this example were as follows:
The results, shown in
The purpose of this experiment is to complete a Measurement System Analysis for the two-step elution process using the BD Viper™ System in extracted mode to determine the reproducibility of results between runs and Viper instruments.
Two-step elution means the addition of 2× KOH solution (142 mM) to extraction tubes followed by 2× neutralization solution to form the SDA assay buffer (2× neutralization solution is 251 mM Bicine, 21.8% DMSO, 19% Glycerol, with 0.1% Tween 20 and 0.03% Proclin 300).
The materials used in this experiment were as follows:
CT/GC positive and negative samples were prepared in Sample Diluent. The low target pool was spiked with CT at 15 EB/ml and GC at 50 cells/ml. The high target pool was spiked with CT at 30 EB/ml and GC at 100 cells/ml. The spiking calculations were as follows:
Low: CT 15 EB/ml: 105/ml (xmls)=15 EB/ml (2450 ml)==>367.5 ul CT spike;
GC 50 cells/ml: 105/ml (xmls)=50 cells/ml (2450 ml)==>1225 ul GC spike.
High: CT 30 EB/ml: 105/ml (xmls)=30 EB/ml (2450 mls)==>735 ul CT spike;
GC 100 cells/ml: 105/ml (xmls)=100 cells/ml (2450 mls)==>2450 ul GC spike.
The CT/GC negative samples were left unspiked. The samples were aliquoted into 5 separate Viper racks at 3.5 ml/tube for 3 extraction events from each tube The same samples were used for all three runs on each instrument. Samples were extracted using either a one-step or two-step elution protocol. In brief, KOH was added to the samples to lyse the cells and liberate their nucleic acid into solution. Binding acid was then added to lower the pH and bring about a positive charge on the surface of the ferric oxide, which in turn bound the negatively charged DNA. The ferric oxide and bound DNA were washed and the DNA was eluted either in a two-step process involving exposure to KOH followed by neutralization with bicine buffer, or in a one-step process involving exposure to a solution of bicine and KOH at approximately pH 8.4. The eluted DNA was then detected using the BD ProbeTec™ CT/GC Q(Amplified DNA Assays.
The results are shown in
The two-step elution process performed better and gave significantly higher CpK values than the one-step elution program for both CT and GC.
Although the foregoing description is directed to the preferred embodiments of the invention, it is noted that other variations and modifications will be apparent to those skilled in the art, and may be made without departing from the spirit or scope of the invention. Moreover, features described in connection with one embodiment of the invention may be used in conjunction with other embodiments, even if not explicitly stated above.
The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/929512, filed Jun. 29, 2007, and U.S. Provisional Patent Application Ser. No. 60/929544, filed Jul. 2, 2007.
| Number | Date | Country | |
|---|---|---|---|
| 60929544 | Jul 2007 | US | |
| 60929512 | Jun 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12165069 | Jun 2008 | US |
| Child | 15461889 | US |
