Patent Grant
8580521
This application corresponds to the national phase of International Application No. PCT/EP2010/051673 filed Feb. 11, 2010, which, in turn, claims priority to European Patent Application No. 09.002105.6 filed Feb. 16, 2009, the contents of which are incorporated by reference herein in their entirety.
The genus Yersinia comprises three human-pathogenic Yersinia spp., Y. pestis, Y. pseudotuberculosis and Y. enterocolitica and eight further species namely Y. aldovae, Y. bercovieri, Y. frederiksenii, Y. intermedia, Y. kristensenii, Y. moolaretti, Y. rohdei and Y. ruckeri, which rather play a role in humans as opportunistic pathogens in the case of wounds and sepsis. Y. pestis causes plague and can be transmitted by fleas from the natural rodent reservoir to humans. Y. enterocolitica and Y. pseudotuberculosis occur in wild and domesticated animals in the temperate to subtropical zones throughout the world. In Germany, the intestinal disease caused by Y. enterocolitica and Y. pseudotuberculosis, called yersiniosis, is, after salmonellosis (Salmonella enterica) and campylobacter enteritis (Campylobacter jejuni), the third most common bacterial enteritis disease notified annually to the Robert Koch Institute (RKI) in Berlin. In Germany, 4987 cases of diseases caused by Yersinia according to the RKI disease classification were reported to the Robert Koch Institute in 2007, and 5162 in the year 2006. The highest age-specific incidence was observed in young children in the age range from 1 to 4 years (RKI). However, the actual frequency of these diseases is not known exactly—many who become ill do not see a doctor if the disease course is subclinical or mild and brief, many diseases are not clarified aetiologically and not all diagnosed cases are reported. It is estimated that up to 43% of blood donors in Germany and 31% of blood donors in Finland have specific antibodies to Yersinia (tested by enzyme immunoassays or immunoblots). This result suggests an unexpectedly high prevalence of yersinioses experienced in industrial countries with high standards of hygiene.
The enteropathogenic Y. enterocolitica and Y. pseudotuberculosis pathogens occur in pigs, sheep, bovines and poultry and enter food (e.g. raw pork) and drinking water mainly via the slaughtering process. Furthermore, cases of transmission to pets have been described. It has also been found that up to 100% of wild boar carry Yersinia enterocolitica in the nasopharyngeal cavity. Yersinia are able to multiply at low temperatures (>4° C.). In the industrial countries, multiplication in refrigerated foods represents the epidemiologically most important form of distribution of Y. enterocolitica and Y. pseudotuberculosis.
The exact infective dose is not known (presumably >10000 bacteria). The incubation time is two to five days after infection. Enteropathogenic Y. enterocolitica and Y. pseudotuberculosis strains generally colonise the intestine-associated lymphatic tissue of the terminal ileum, in the so-called Peyer's patches (continuous aggregation of lymphatic follicles). Following colonisation, the Yersinia overcome, via so-called M cells in the follicle-associated epithelial cell layer of the Peyer's patches, the gastrointestinal barrier of the organism and spread via the draining lymphatic vessels in the mesenteric lymph nodes. Y. enterocolitica then attacks and damages further regions of the intestine, which explains the typical tissue damage of the small intestine and colon in yersiniosis patients. Y. pseudotuberculosis shows a course of infection similar to that of Y. enterocolitica, except that mesenteric lymph nodes, liver and spleen are more often affected and enteritis symptoms and excretion via the intestine are much less than with Y. enterocolitica.
The enteritic form of Yersinia infections, also called yersiniosis, is limited, in uncomplicated cases, to the gastrointestinal tract and is characterised by watery diarrhoea for several days (called acute Yersinia gastroenteritis). However, depending on patients' age, immune status, histocompatibility type (HLA-B27) and sex, yersinioses can display different courses and symptoms, for example fever, nausea, colic-like lower abdominal pains (pseudoappendicitis), muscular pains and headaches and inflammations in the pharyngeal region (pharyngitis), in the mesenteric lymph nodes (acute mesenteric lymphadenitis) and in the ileum and colon (Yersinia ileitis and colitis). In uncomplicated cases, the disease abates after a few days or at the latest after two weeks.
In patients with underlying diseases, for example diabetes mellitus, liver cirrhosis, iron storage diseases (dialysis patients, thalassaemia) or immunosuppression, extraintestinal infections may occur (e.g. septic forms). Not uncommonly, septic shock with high lethality (approx. 75%) occurs after blood transfusion with Yersinia-contaminated banked blood.
Apart from the intestinal and extraintestinal forms of yersiniosis, in which the causative agent can generally be isolated, in up to 30% of cases there are also concomitant or secondary diseases, generally with an aseptic course. The most common secondary disease is HLA-B27-associated reactive arthritis [abbreviation: ReA] (about 60-80% of ReA cases are HLA-B27-positive). ReA starts approx. 1-4 weeks after onset of the intestinal symptoms (but often without preceding intestinal symptoms). Most often it is the joints of the lower extremities that are affected. In most cases the symptoms abate after approx. 3-12 months, but a chronic or relapsing course may also develop. Other complications that often occur after yersiniosis are inflammations of the thyroid (thyroiditis), of the heart muscle (myocarditis) and of the kidneys (glomerulonephritis), reddening of the skin (erythema) of the lower extremities (Erythema nodosum) and acute or chronic enlargement of the lymph nodes (lymphadenopathies) or of the spleen (splenomegaly).
In yersinioses without further immunological complications, for example reactive arthritis, the symptoms generally abate after a short time. Therefore in most cases it is unnecessary to treat a Yersinia infection with antibiotics. In the case of a septic course or persistent symptoms, differential treatment with antibiotics is necessary. Owing to the frequently occurring beta-lactamases with Yersinia, infections with Y. enterocolitica or Y. pseudotuberculosis are treated pathogen-specifically with gyrase inhibitors, tetracycline, trimethoprim/sulfamethoxazole etc.
Related Yersinia species (e.g. Y. enterocolitica and Y. pseudotuberculosis) are differentiated biochemically. Y. pseudotuberculosis forms a biochemically uniform group, which is divided into eight serogroups, of which the serovars I, II and III are of importance in human medicine in Europe (Bottone, [1997] Clin. Microbiol. Rev., 10, 257-276). In contrast, Y. enterocolitica is an extremely heterogeneous species both biochemically and serologically, with pathogenic and non-pathogenic, geographically separate subgroups. Y. enterocolitica is divided into six biovars (BV)/biotypes with different biochemical effects (1A, 1B, 2, 3, 4, 5) and approx. 60 serovars (with different O and H antigens) (Wauters et al., [1987] Contrib. Microbiol. Immunol., 9, 14-21). Whereas biovar 1A Yersinia mainly occur in the environment, the known human-pathogenic Y. enterocolitica strains belong to BV 1B (serotypes O:8, O:4, O:13, O:18, O:20, O:21, occurring mainly in the USA), BV 2 (Europe [O:9], USA, Japan [O:5, 27]), BV 3 (O:9 and O:5, 27) and BV 4 (Europe and USA [O:3]). (Bucher et al., [2008] Foodborne Pathog. Dis., 5, 273-280). Approximately 80-90% of reported cases of Yersinia gastroenteritis in Germany are caused by Y. enterocolitica serotype O:3 (RKI).
The virulence of the enteropathogenic Yersinia (Y. enterocolitica biovars 1B, 2, 3, 4 and 5, Y. pseudotuberculosis) and of the plague-causing Y. pestis is due to a highly conserved virulence plasmid pYV with a size of 65-70 kb (in Y. pestis pCDI). These virulence factors enable pathogenic Yersinia to survive in the host's lymphoid tissue. The Y. enterocolitica biovar 1A does not carry a pYV plasmid and is therefore regarded as non-pathogenic.
The pYV plasmid codes for the membrane protein YadA (Yersinia adhesin) and a number of so-called Yersinia outer proteins (Yops) and the associated secretory apparatus (T3SS), which is called Ysc (Yop secretion). As substrate of T3SS, the Yops are injected as anti-host effectors into eukaryotic cells (e.g. in macrophages). The protein complex of T3SS consists of 27 proteins with known or unknown functions, for example a regulatory function (YopQ, YopN), translocation function (YopB, YopD) and effector function (YopH, YopE, YopT, YopP, YopO). The adhesin YadA is also encoded on the virulence plasmid. It mediates the adhesion of the pathogens on host cells and enables the Yops to inject into the target cells. The so-called V antigen (LcrV) is also encoded on the pYV plasmid. This antigen forms the tip of the Ysc injectisome, regulates Yop secretion and modulation of the host's immune system.
The virulence of the Yersinia is also influenced by chromosomally encoded factors, in addition to the plasmid-encoded virulence factors. Adhesion of Yersinia on epithelial cells of the intestine requires among other things the presence of the invasin Inv and of the adhesin Ail (the “attachment invasion locus” of Y. enterocolitica), which can be expressed by all enteropathogenic Yersinia.
Other known chromosomally encoded pathogenicity factors are e.g. the secreted and thermally stable enterotoxin Yst, the so-called “mucoid Yersinia factor” MyfA of Y. enterocolitica, or the homologous pH 6 antigen PsaA of Y. pseudotuberculosis and Y. pestis, the yersiniabactin-siderophore system encoded on the so-called high-pathogenicity island (HPI) (FyuA receptor with Irp1-9), the Ysa Type-III secretory apparatus, the lipopolysaccharide LPS that is characteristic of all Gram-negative bacteria, the enzyme urease and the toxin complex TC that is active against insects (tcbA, tcaC, tccC).
The MyF fibril system consists of the three subunits MyfA, MyfB and MyfC. The fibril is constructed from MyfA subunits, whereas MyfB and MyfC form the transport and structuring apparatus. The MyfA surface antigen with a size of approx. 17 kDa is expressed in vitro during the early stationary growth phase, and full expression only takes place at 37° C. in an acid environment (pH 6). The myfA gene is present in human-pathogenic Y. enterocolitica strains (e.g. O:3, O:4, O:8; O:9) and in approx. 16% of non-human-pathogenic Y. enterocolitica BV 1A strains and shows a significant link to virulence. Leiva et al. showed, in coagglutination experiments with sera from rabbits that had been immunised intravenously with live Y. enterocolitica or Y. pseudotuberculosis strains, that the antisera obtained against MyfA (Y. enterocolitica) or PsaA (Y. pseudotuberculosis) allow bacteriological differentiation between Y. enterocolitica (MyfA) and Y. pseudotuberculosis (PsaA) strains (Leiva et al., Contrib. Microbiol. Immunol., 13, 158-164). These immunisation experiments also show that MyfA or PsaA are produced under laboratory conditions, i.e. under controlled nutrient conditions (growth medium) and temperature and pH conditions, and induce the production of the serum antibodies in intravenously immunised rabbits. However, a serodiagnostic application in humans is not under consideration. In particular, as the natural function of the antigens is unknown, it can also not be expected automatically that the MyfA or PsaA antigens are expressed during natural infection in the human gastrointestinal tract by pathogenic Yersinia. Additionally it has to be borne in mind that data from animal experiments can seldom be applied to the diagnostic situation in humans, because as is well known, the production of antibodies in animals can differ from that in humans.
The Psa-antigen complex (pH6 antigen) of enteropathogenic Y. pseudotuberculosis was originally characterised in the plague-causing Y. pestis as fimbriated structure with a diameter of 3-5 nm. The PsaA subunits are arranged on the bacteria surface by the translocation and structuring apparatus, which consists of PsaB and PsaC. The antigen domain PsaA, with a size of approx. 17 kDa, shows approx. 44-47% amino acid sequence homology with the Y. enterocolitica-homologous MyfA. As with MyfA, the production of PsaA in Yersinia is induced under laboratory conditions by temperature (37° C.) and slightly acid pH (pH 6). The PsaA deletion mutant strains of Y. pestis show a significantly reduced virulence in vitro and in vivo.
The observations that MyfA and PsaA antigens are expressed under laboratory conditions only at 37° C. and at acid pH, and that an immune response can be produced in laboratory mice and rabbits after infection with precultured (in vitro) Yersinia strains, leads to the presumption that these proteins might have a function during infection or might be expressed in the acidic environment of the intestinal tract. However, the exact functions of Myf and Psa during Yersinia infection, and therefore the importance of these antigens for Yersinia pathogenesis, are still unknown.
The classical diagnosis of the acute yersiniosis diseases is based primarily on detection of the pathogen in the stool, e.g. by means of cold enrichment, selective culture medium (e.g. so-called cefsulodin-Irgasan™-novobiocin agar culture medium [CIN-agar]), biochemical properties (e.g. so-called API E20 test; bioMerieux, Paris, France) and the detection of pathogen-specific nucleic acids (DNA) by polymerase chain reaction (PCR). Detection of the microbe in the stool may be possible for a period of 2 to 12 weeks. After the diarrhoea symptoms have subsided, Yersinia are typically no longer detectable in the stool.
Serology, i.e. detection of the individual serum antibody response to Yersinia-specific O and H antigens (so-called Widal and passive haemagglutination tests), virulence-associated proteins (e.g. by enzyme-linked immunosorbent assay [ELISA] and immunoblotting) or bacterial ultrasonicate (by means of complement-fixation reaction [CFR]), is suitable according to current standards for supplementary diagnosis of acute infection.
However, serodiagnostics is essential for clarifying secondary diseases, for example reactive arthritis, because direct detection of the pathogen, mostly after the acute infection has subsided, is not possible. The present invention relates to diagnostic devices, by means of which an infection with Yersinia enterocolitica can be differentiated serologically from an infection with Yersinia pseudotuberculosis.
In an acute Yersinia infection, typically the Yersinia-specific immunoglobulin (Ig) classes IgM, IgA and generally also IgG are detectable. In the course of infection, the specific IgM and IgA response is attenuated within 3-6 months (persistence of IgM: approx. 1-3 months and IgA: approx. 2-4 months), whereas Yersinia-specific IgG antibodies can persist for several years, possibly even life-long (in 80% of patients after a Yersinia infection). In chronic Yersinia infection and Yersinia-induced reactive arthritis, persistent IgA antibodies can be detected for years, along with Yersinia-specific antibodies of the IgG class. The Yersinia-specific antibodies of the IgM class are mostly no longer detectable in secondary diseases.
The conventional serological methods of detection, such as the Widal and complement-fixation reaction directed against whole cell lysates, only possess low diagnostic sensitivity and specificity owing to cross-reactivity with a large number of human pathogens (for example Bartonella henselae, Borrelia burgdorferi, Chlamydia pneumoniae, Rickettsia rickettsii, Escherichia coli, Brucella spp., Salmonella spp.). Therefore enzyme immunoassays (ELISA) and immunoblots are currently preferred for the detection of IgG, IgA and IgM antibodies to recombinantly produced virulence-associated Yersinia-specific antigens (e.g. Yops and V-AG).
Existing Yersinia serodiagnostics is based mainly on the reaction for detecting the IgG and IgA (conditionally also IgM) response to virulence plasmid pYV secreted Yop proteins, for example YopD, YopH, YopM, YopE, V-AG and YopN. The specificity and sensitivity of these Yop antigens is, however, in need of improvement and is supplemented according to the invention with additional Yersinia-specific antigens.
In addition, owing to the similarity of the aetiology and of the process of infection, a subclinical course of infection or a nonspecific symptomatology and a high infection rate, it is difficult to differentiate between Y. enterocolitica and Y. pseudotuberculosis infections or secondary diseases caused by these pathogens (for example ReA or post-enteritic arthritis, myocarditis, glomerulonephritis, lymphadenopathies, splenomegaly, erythema nodosum) with the conventional diagnostic test methods. However, a method for specific serological detection (i.e. in particular differentiating between the most common human-pathogenic Yersinia species Y. enterocolitica and Y. pseudotuberculosis) is necessary, so as to be able to provide early and effective treatment of yersinioses or prevention of secondary diseases (i.e. adequate antibiotic therapy). The different proteins of Y. enterocolitica (MyfA) and Y. pseudotuberculosis (PsaA) can make a contribution to this.
Heesemann et al. (Microbial Pathogenesis [1988], p. 437-447) describe the immune response of orally infected rabbits to virulent (pYV plasmid) and non-virulent (no pYV plasmid) serotype O:3 strains of Yersinia enterocolitica, which had been precultured overnight in neutral growth medium (BHI). It is unlikely that the MyfA antigen was expressed under these conditions owing to neutral pH and the growth phase. In addition the presence of the PsaA antigen is ruled out (the authors only used Y. enterocolitica strains). The antigens were separated using SDS-electrophoresis and were investigated further by Western blotting. No further purification was carried out. Moreover, the authors stated that this method is rather unsuitable as such for diagnostic purposes, owing to high cross-reactivity with intestinally pathogenic Escherichia coli and Salmonella strains.
Tomaso et al. (European Journal of Epidemiology [2006], 21: 77-81) and Stolck-Engelaar et al. (Scand. J. Infect. Dis. [1996], p. 571-575) describe the seroprevalence of anti-Yersinia antibodies in healthy Austrians and in Dutch yersiniosis patients. Determination is carried out with a commercial Western Blot assay with the antigens Yop M, Yop H, V-Ag, Yop D and Yop E. The antigens MyfA or PsaA are not used.
The only method based on the MyfA and PsaA antigens proposed to date was described by Leiva et al., 1995. However, this related to a bacteriological detection method for identifying pathogenic Yersinia strains after growing the cells on an agar culture medium.
The present invention relates to a device in the broader sense for serological differentiation of an infection with Yersinia enterocolitica from an infection with Yersinia pseudotuberculosis. “Serological differentiation” in the sense of the present application means that, on the basis of a sample obtained from blood (serum, plasma), it is possible to determine by means of an immunological assay whether it is an infection caused by a strain of Yersinia enterocolitica or Yersinia pseudotuberculosis. Said device contains at least one antigen selected from a group of antigens that can be classed with the outer surface proteins or secreted proteins of Yersinia. At least one of these antigens must be used in the device, and it is not absolutely essential to use the complete protein—it may be perfectly sufficient to use protein fragments that have a diagnostically relevant epitope.
According to the invention, the antigens are used in essentially pure form, and this is preferably achieved by producing the antigens recombinantly rather than isolating them from cell lysate.
A fragment of one of the antigens listed below, which has at least eight consecutive amino acids, preferably at least 12, more preferably at least 20, even more preferably at least 30 consecutive amino acids and quite particularly preferably at least 50 consecutive amino acids, is sufficient. In a preferred embodiment the peptides have 10 to 30 consecutive amino acids. Each peptide/fragment has at least one diagnostically relevant epitope.
When selecting the fragments, a region is selected that contains at least one diagnostically relevant epitope. The epitope regions can be localised by standard methods known by a person skilled in the art. It is possible to determine the hydrophilicity/hydrophobicity of the protein using suitable computer programs. Hydrophilic regions are as a rule predestined to carry suitable epitopes, because in the folded protein the hydrophilic regions end up on the surface. Hydrophobic regions are more likely to be localised in the interior of the folded protein and are therefore unlikely to be involved in diagnostically relevant epitopes. The epitopes are preferably linear epitopes, but conformation epitopes can also be used advantageously.
When suitable regions have been identified, these can either be synthesised by chemical synthesis or produced by recombinant methods. These proteins or peptides can then be reacted with suitable blood, serum or plasma samples, whose aetiology has been determined with other, medical parameters. In this way, a person skilled in the art can localise suitable epitopes.
The devices according to the invention thus contain at least one antigen or a fragment of one of these antigens selected from the group consisting of antigens listed hereunder. These are the following antigens:
In addition to the antigen from the first group of antigens, the device according to the invention also has at least one of two further proteins, namely either the protein MyfA and/or the protein PsaA or fragments of one of these two proteins. Once again the fragments have a minimum size of at least 8 consecutive amino acids, preferably at least 12 consecutive amino acids, more preferably at least 20, particularly preferably at least 30 and quite particularly preferably at least 50 consecutive amino acids of one of the proteins MyfA and/or PsaA.
It is preferable for the device to have the two complete proteins MyfA and PsaA or fragments thereof together, wherein the individual antigens are spatially separate from one another. The amino acid sequences of the two proteins MyfA and PsaA (without leader sequence) are shown below.
MEPTVINSKDISATKTVKEGGSFSVEFKATENEIVSGKLDADTPAFHL
MSTVINSKDVSGEVTVKQGNTFHVDFAPNTGEIFAGKQPGDVTMFTLT
The proteins MyfA or PsaA are encoded by the nucleotide sequences MyfA or PsaA shown below and can be produced recombinantly using suitable vectors and host cells.
The individual antigens are, according to the invention, arranged spatially separately from one another in the test device or the test kit. In the case of Western Blots, for example, the antigens can be applied in the form of bands on the carrier material, wherein the individual antigens are in each case present in a particular, well-defined band. This spatial separation of the individual antigens can also be achieved if the antigens are applied spatially separately from one another in a line-assay. However, it is also possible to apply the individual antigens on a microtitre plate, so that only one antigen is present in each well. In an alternative embodiment, in each case an antigen is applied on a type of carrier (for example spheres), so that only one antigen is bound to each carrier. As an alternative, the antigens can be applied to assay plates (microchips), wherein the individual antigens are fixed on specified points on said chips.
According to the invention, first it is determined, by reaction with at least one, or even a plurality of antigens selected from the group Yop D, Yop H, Yop M, Yop E, V-AG and/or Yop N, whether it is a Yersinia infection. If the result of this test is positive, it is determined, using the antigen MyfA and/or PsaA, whether the infection is caused by Yersinia enterocolitica or Y. pseudotuberculosis. The individual detection steps can be carried out either simultaneously or successively.
A device for serologically detecting an infection by Yersinia species is, according to the invention, in a preferred embodiment a diagnostic kit. This is to be understood as a device that is used by diagnostic laboratories for serological diagnosis. In a preferred embodiment the antigens are bound spatially separately from one another on a carrier matrix, for example wells of a microtitre plate, spheres, nitrocellulose or nylon. The antibodies (mainly of classes IgG, IgM and IgA) present in a sample from a patient (e.g. blood, serum, plasma, saliva) react with the bound antigens and so are immobilised. In a preferred embodiment these are diagnostic kits, wherein ELISA assays represent a preferred embodiment. In the case of ELISA assay kits, usually the antigen is bound to the wells of a microtitre plate. The specific antibodies present in the samples can react with the antigens. The antibodies from serum or plasma, which have bound specifically to the antigens present in the wells, are as a rule detected with anti-antibodies, which carry a marker, preferably an enzyme marker.
Another preferred embodiment of the device according to the invention comprises so-called line-tests. In this case, a plurality of antigens are applied on the test strips according to a predetermined pattern. The blood samples to be investigated (sera or plasmas) are reacted with the test strips and antigen-antibody reactions are detected by enzyme-labelled antibodies and subsequent colour reaction. A conclusion can be drawn about the infection or infective agent from the specific pattern of the reactivities or colour signals.
The device according to the invention can also be an immunoblot or Western blot. In this case, the diagnostically relevant proteins are first separated according to size for example by diffusion, capillary action or electrophoresis and transferred to a carrier material, for example a nylon membrane or a nitrocellulose membrane, and fixed there. This carrier material with the proteins or protein fragments bound thereto is reacted with the patient's blood samples (serum or plasma).
The immobilised specific antibodies can for example be detected by reaction with an anti-antibody. Preferably various anti-antibodies can be used, which react either with IgG, IgM or IgA. This makes further differentiation of the immune response possible. As a rule these anti-antibodies carry a marker. This can be an enzyme, which catalyses a colour reaction, but it can also be fluorescent residues or radioactive residues. What is important is that antibodies bound to antigens can be detected with the anti-antibodies.
In another embodiment, the device according to the invention is a bead-based assay. A known commercial application of these bead-based microarrays is the Luminex-XMAB technology from Luminex Corporation (Austin, USA). This system uses microspheres (so-called beads) and evaluation is based on flow cytometry. In the case of fluorescence-labelled embodiments, the antigens according to the invention can be fixed on beads and the binding of the antibodies to the antigens is visualised with suitable labelling, e.g. fluorescence.
Another preferred embodiment of the device according to the invention relates to protein microarrays. In this case various antigens are fixed in a narrow space on a surface. As it is known which antigen is present in which place, after visualisation of the antigen-antibody reaction for example by means of a colour reaction or fluorescence labelling, it is also possible to state which antigen has reacted with the antibodies in the serum.
Usually the individual antigens are fixed in the device in such a way that after the reaction it is possible to establish with which particular antigen the antibodies present in the sample have reacted. In an ELISA assay, for example, the individual antigens are put in different cavities of the microtitre plate. In the line-assay, the antigens are sprayed on different strips of the carrier material and in the case of bead and planar microarrays the respective antigens are always applied at a defined place on the carrier or defined beads. The devices according to the invention are used for detecting human-pathogenic Yersinia species or subspecies. By combining different antigens, on the one hand it is possible to perform sensitive and specific detection of the pathogens and on the other hand, in a preferred embodiment a differential-diagnostic detection is also possible, wherein it is possible to distinguish between an infection caused by Yersinia enterocolitica and an infection with Yersinia pseudotuberculosis.
Another essential aspect of the present invention is also that serological detection or serological differentiation is possible when the acute Yersinia infection has already abated. For treating these secondary diseases it is essential to be able to determine which bacterium (Yersinia enterocolitica or Yersinia pseudotuberculosis) caused the original infection.
The device according to the invention thus has at least two different antigens, wherein one antigen is selected from the group consisting of the antigens YopD, YopH, YopM, YopE, V-AG and YopN described in more detail above. The other group comprises the antigens MyfA and PsaA.
In a particularly preferred embodiment the device comprises the antigen YopD and the antigen YopH together with either MyfA or PsaA.
In a still further preferred embodiment the device according to the invention comprises the antigens YopD, YopH, YopM and either MyfA or PsaA, the combined use of MyfA and PsaA being quite particularly preferred, however.
In a particularly preferred embodiment the device according to the invention thus has the proteins MyfA and/or PsaA or fragments thereof, as defined above, together with the following protein or protein combinations, wherein these proteins can also be in the form of fragments, as defined above. The device according to the invention has at least the protein YopD, which is preferably used together with YopH and more preferably together with YopM combined with MyfA and/or PsaA.
Another preferred embodiment comprises the proteins or fragments of YopD, YopH, YopM and YopE together with MyfA and/or PsaA.
Another preferred embodiment comprises the proteins and/or fragments of YopD, YopH, YopM, YopE, V-AG together with MyfA and/or PsaA.
Another preferred embodiment comprises a combination of proteins and/or fragments with the following designations: YopD, YopH, YopM, YopE, V-AG, YopN, and MyfA and/or PsaA.
The stated antigens can also be used in the form of fragments thereof, wherein the fragments have a serologically relevant epitope. When, according to the invention, fragments of the antigens are used, in the case of the antigen MyfA, on the one hand the N-terminal fragment with the amino acids 30-41 and on the other hand the C-terminal fragment with the amino acids 148-159 is particularly preferred. In the PsaA protein, the fragments that comprise the amino acids 27-37 (N-terminus) and 144-155 (C-terminus) are particularly preferred. In this case fragments are used which comprise this amino acid sequence and which have the sizes defined in more detail above.
The present invention thus relates to the use of an antigenic protein MyfA or a fragment thereof, as defined in more detail above, either alone or together with the antigenic protein PsaA or a fragment thereof, as defined above, for serologically detecting an infection caused by Yersinia or an infection caused by Y. enterocolitica or Y. pseudotuberculosis. This differentiation is clinically important, because an infection caused by Yersinia enterocolitica can be treated differently from an infection caused by Yersinia pseudotuberculosis.
With the device according to the invention, it is possible to detect Yersinia, which are of great importance, as they are pathogenic for humans. The Yersinia occur in farm animals, for example pigs and poultry, and on infection can cause a disease in humans. It can therefore be of considerable medical and epidemiological importance to detect, by means of a simple and relatively inexpensive test kit, the course of the chains of infection. This allows conclusions to be drawn about the sources of the pathogens and these can be identified and possibly be made harmless. It is thus possible to detect and differentiate the pathogens of yersinioses.
The results that can be achieved with the detection according to the invention are surprising, because it could not automatically be assumed that the antigens MyfA and/or PsaA are also expressed in sufficient amounts for antibody formation in the human body under real infection conditions. Furthermore, it was not known that specific antibodies of the IgG, IgM and IgA class against MyfA and PsaA antigens are formed in humans.
Based on the relatively high protein homology (44%) between MyfA and PsaA antigens and the already described interspecies homology or interspecies cross-reactivity between non-pathogenic Yersinia strains and other enterobacteria, for example E. coli and Salmonella species, it was not to be expected that the MyfA or the PsaA antigen can be used for differentiating the infective agent. The detection or differentiation is preferably performed with human blood, in particular serum or plasma. Determination is, however, also possible with cerebrospinal fluid or saliva.
In a quite particularly preferred embodiment the sample to be investigated is on the one hand reacted with an antigen selected from the group Yop D, Yop H, Yop M, Yop E, V-AG and Yop-N, quite particularly preferably with Yop D. If this does not result in a positive reaction and otherwise there is no special further suspicion, this can conclude the diagnosis.
Conversely, if the sample to be investigated reacts positively with this antigen, in particular Yop D, in a further diagnostic step the sample to be investigated can be reacted with the antigen PsaA and/or MyfA, preferably with both antigens. Furthermore, it is useful to differentiate the antibodies found, as to whether they are IgG or IgA antibodies. If the IgM or IgA finding is negative, but the IgG finding is positive, presumably an infection has come to an end.
If the IgM or IgA finding, preferably IgA finding, is positive, there may be an acute infection or a secondary disease. The infection is caused by Yersinia enterocolitica if the IgG, IgM or IgA reaction, preferably IgG finding, is positive with MyfA. If there is a positive reaction with PsaA, it is an infection with Yersinia pseudotuberculosis.
The figures clarify preferred embodiments of the present invention and explain the results obtained in the examples.
In Silico Determination of the Immunogenic Domains of the MyfA and PsaA Antigens
Determination of the homologous antigen regions that might be responsible for the immunogenic reactivity or cross-reactivity of the MyfA and PsaA antigens, was carried out in silico by means of direct amino acid sequence comparison (see
The antigenicity index and the hydrophilic character of the antigen regions was determined in silico with the algorithms of Jameson and Wolf (Comput. Appl. Biosci. (1988) p. 181-186) or of Kyte and Doolittle (Kyte and Doolittle, (1982) J. Mol. Biol., 157, p. 105-132) (
Complete Total Protein Sequences:
MNMKKFVKKPLAIAVLMLASGGMVNMVHA
EPTVINSKDISATKTVKEGGSFSVEFKATENEI
MKMKCFAKNALAVTTLMIAACGMANASTVINSKDVSGEVTVKQGNTFHVDFAPNTGEIFAG
Experimental Determination of the Immunogenic Domains of the myfA Antigens
Preparation of the myfA Partial Fragments
Four fragments were prepared starting from the complete reading frame of the MyfA antigen (Example 1). Both the complete reading frame including the leader peptide and N-, C-, and N- and C-terminally shortened partial fragments are shown (
Specific amplification of the myfA partial fragments was carried out by PCR with chromosomal DNA from Y. enterocolitica serotype O:3/4 (Y. enterocolitica subsp. palearctica strain Y-11; DMSZ 13030) as templates.
The resulting amplificates were cleaved enzymatically with restriction endonucleases and ligated into a suitable vector, pET21-b, which had been cut with the same restriction endonucleases as the amplificates. After transformation of the ligation preparation into a suitable E. coli strain, e.g. BL21 pLys, individual clones were tested for the presence of myfA and psaA by agarose-gel electrophoresis of enzymatically cleaved plasmid DNA and then sequenced. In addition, the expression of the partial fragments was identified and characterised by analysis of the expression products by SDS-polyacrylamide-gel electrophoresis with subsequent Coomassie Blue staining or subsequent transfer to nitrocellulose followed by immunological detection. The fusion proteins were purified by Ni-NTA column chromatography according to the manufacturer's information (the company Qiagen).
In addition to the complete reading frame of MyfA (MyfA;
The following oligonucleotide primers were used for preparing the sequences.
The following primer combinations were used:
Verification of Antigenicity
The immunological reactivity/antigenicity of the MyfA fusion proteins (Example 2) was tested by immunoblot (
The proteins could be detected by detecting the His-tags with a nickel-NTA conjugate from rabbit (very weak reaction, no double bands). The immunoblot with an anti-Y. pseudotuberculosis serum from rabbit did not show any reaction.
The immunological reactivity/antigenicity of the purified MyfA total protein (MyfA) and of the purified MyfA partial fragments MyfA 1-441, MyfA 121-441 and MyfA 121-447 (Example 1,
The blood samples taken before infection showed no reactivity with the antigens of the assay (i.e. YopD, YopH, MyfA, MyfA 1-441, MyfA 121-441, MyfA 121-447, PsaA). After the experimental infection, all four samples reacted with the Yersinia-specific antigens YopD and YopH (
Preparation and Purification of the Recombinant MyfA and PsaA Antigens
MyfA (pmyfA MIK) and PsaA (ppsaA-MIK) expression clones were prepared starting from the complete reading frames (Example 1) of the two antigens. The following oligonucleotide primers were used for preparation of the sequences. The proteins were prepared without leader sequence (MyfA AA 1-29 and PsaA AA 1-26; Example 1), as preliminary experiments had shown that the leader peptide causes reduced expression.
Specific amplification of the myfA fragment was performed by PCR with chromosomal DNA from Y. enterocolitica serotype O:3/4 (Y. enterocolitica subsp. palearctica strain Y-11; DMSZ 13030) as template. The psaA fragment was amplified with chromosomal DNA from Y. pseudotuberculosis serotype 1A.
The resulting amplificates were enzymatically cleaved with restriction endonucleases Nde I and Bam HI and were ligated into a suitable vector, pET3c (New England Biolabs). After transformation of the ligation preparation into the E. coli strain UT 5600 (Elish et al. [1998] J. Gen. Microbiol., 134, p. 1355-1364) the clones were tested for the presence of the myfA and psaA fragments by agarose-gel electrophoresis of enzymatically cleaved plasmid DNA and by DNA sequencing (see below). In addition, the expression of the antigens was identified and characterised by analysis of the expression products MyfA-MIK and PsaA-MIK by SDS-polyacrylamide-gel electrophoresis followed by Coomassie Blue staining or subsequent transfer to nitrocellulose followed by immunological detection.
The recombinant proteins MyfA-MIK and PsaA-MIK were purified by anion-exchange and cation-exchange column chromatography. An anion exchange (Q-Sepharose Fast Flow; GE Healthcare, Munich, Germany) was performed in the first step, a cation exchange (S-Source 15; GE Healthcare) in the second step and an anion exchange (Q-Source 30; GE Healthcare) in the third step. The individual purification steps and/or the purified protein were verified by SDS-polyacrylamide-gel electrophoresis with subsequent Coomassie Blue staining or subsequent transfer to nitrocellulose followed by immunological detection and were characterised with respect to the degree of purity, possible protein cleavage and immunological reactivity.
DNA Sequencing of the pmyfA-MIK and ppsaA-MIK Expression Clones and Resultant Protein Sequences (AA) MyfA-MIK and PsaA-MIK
The START (atg) and STOP (uaa) codons are marked in black.
DNA Sequences
atggaaccgactgttattaatagtaaagacatctctgcaacaaaaactgttaaagagggaggttcgttctcagttgaattcaaggc
atgtctactgtcattaactccaaggatgtttctggtgaggtgactgtcaagcagggaaacacattccacgtcgattttgcgcctaa
Amino acid sequences (AA)
MEPTVINSKDISATKTVKEGGSFSVEFKATENEIVSGKLDADTPAFHL
MSTVINSKDVSGEVTVKQGNTFHVDFAPNTGEIFAGKQPGDVTMFTLT
Serological Differentiation of Yersinioses Caused by Y. enterocolitica or Y. pseudotuberculosis
Two human serum samples were defined by Widal reaction as anti-Y. enterocolitica serotype O:3 (LYE16)- or as anti-Y. pseudotuberculosis (LYE01)-IgG-positive.
Comparison of the serological IgG reactivity of Yop, MyfA-MIK and PsaA-MIK antigens (Example 3) by means of line-assays showed that the Y. pseudotuberculosis-positive serum sample reacted very strongly with YopD and PsaA. In contrast, the anti-Y. enterocolitica-IgG-positive sample reacted with the antigens YopM, YopH, V-AG, YopD, YopN, YopE and MyfA. This serum sample also showed very weak reactivity with PsaA.
There is thus an indication that the antigens MyfA-MIK and PsaA-MIK make possible the serological differentiation of Y. enterocolitica and Y. pseudotuberculosis infections.
Comparison of the Serological Prevalence of the Anti-Yop, Anti-MyfA and Anti-PsaA Antibodies of the IgG, IgM and IgA Class in Serum Samples from Bavarian Blood Donors or in Serum Samples from Finnish and German Yersiniosis Patients
The IgG, IgM and IgA response to recombinantly produced YopM, YopH, V-AG, YopD, YopN, YopE, MyfA-MIK and PsaA-MIK (Example 4 and 5) antigens with sera from three different sera collections (i.e. Bavarian blood donors n=40; Bavaria; Germany, yersiniosis patients from Finland [KTL, n=18] and yersiniosis patients from Germany [YeD, n=23]) were investigated by line-assays. The recomLine Yersinia from the company Microgen GmbH was used as reference test.
Blood Donor Sera
48% (n=19) of the tested blood donor sera from Bavaria (n=40) showed IgG reactivity with YopD (
As the sera were obtained from healthy donors, IgM antibodies to YopD could not be detected in any of the sera tested (Table 1). Three Yop-IgG-positive sera (n=19) had an isolated IgM titre directed against YopH (n=2; 11%; serum No. 1087: high IgG titre against YopD and PsaA; serum No. 1099: high IgG titre against YopD) or PsaA (n=1; 5%, serum No. 1083: high IgG titre against YopD, MyfA-MIK and PsaA-MIK). None of the samples tested reacted with MyfA-MIK (Table 1).
Seven YopD-IgG-positive serum samples from blood donors (n=19) showed an IgA titre against YopD (Table 1). Three of the sera tested reacted with PsaA-MIK. Interestingly, the Yop-IgG-negative serum sample No. 1080 showed a very weak isolated reactivity with PsaA. The YopD and PsaA-MIK IgG-high positive serum samples No. 1096 and No. 1110 also had a strong (serum No. 1096) or weak (serum No. 1110) IgA response to PsaA-MIK (Table 1). None of the samples tested reacted with MyfA-MIK (Table 1). Based on the parallel occurrence of anti-IgA-reactivity to the YopD, Yop-N and PsaA antigens in the samples No. 1110, it is to be expected that this is a diagnostically relevant serological finding, for example recent Y. pseudotuberculosis infection or occurrence of reactive arthritis.
Sera of Yersiniosis Patients from Finland
17 (90%) of the sera tested from patients with suspected Yersinia-induced reactive arthritis from Finland (n=18) showed an IgG response to YopD (
15 (88%) of the sera tested had IgM antibodies to YopD (Table 2). One serum (No. 52) also showed a strong IgM response to PsaA-MIK (Table 2).
17 serum samples from yersiniosis patients (n=18) had an IgA titre against YopD (Table 2). Three of the sera tested also reacted with PsaA-MIK (No. 23, 24 and 40; Table 2).
Sera of Yersiniosis Patients from Germany
All (n=23) sera tested of yersiniosis patients from Germany showed an IgG reactivity with YopD (
A low IgM response to YopD was only detected in two (9%) of the sera tested (n=23), and to YopE in three sera (Table 3). One serum, No. 986, reacted very strongly with PsaA-MIK (Table 3).
All sera tested from yersiniosis patients had an IgA response to YopD (Table 3). One of the samples also reacted with MyfA-MIK (serum No. 976) and another with PsaA-MIK (serum No. 1025). These sera also showed a strong IgG response to MyfA-MIK or PsaA-MIK (Table 3).
Interestingly, the two tested collections of samples from yersiniosis patients from Finland and Germany differ in anti-MyfA- and anti-PsaA-IgG prevalence. Owing to low isolation rate or technically difficult cultivation and isolation of the Y. pseudotuberculosis strains, at present no reliable epidemiological data are available.
Diagnostic Relevance of the PsaA-MIK and MyfA-MIK Antigens in the Diagnosis of Acute Y. pseudotuberculosis Infections
The abbreviation “MIK” indicates that the antigens are produced recombinantly by the applicant.
The PsaA-MIK and MyfA-MIK antigens were used in a bead-based assay system (Luminex) for detecting IgG, IgM and IgA reactivity to the PsaA-MIK or the MyfA-MIK antigen. A collection of serum samples from patients who had acute yersiniosis caused by Yersinia pseudotuberculosis (K. Jalava, P. Nuorti: “Porkkanaraasteesta laaja Yersinia pseudotuberculosis-epidemia, Kansanterveyslehti, 2003) was used. Eight Y. enterocolitica IgG-positive (determined with so-called Widal haemagglutination test and a blot assay) and 19 Y. enterocolitica-negative routine samples were used as negative comparison group. The results are presented in Table 4.
96.9% (63 samples from 65 samples tested) of the tested Y. pseudotuberculosis patient samples showed high IgG reactivity to the PsaA-MIK antigen. Only three of the samples tested reacted in parallel to both antigens (MyfA-MIK and PsaA-MIK). 44.6% of the samples had anti-PsaA-MIK-IgM reactivity and 58.5% of the samples had anti-PsaA-MIK-IgA reactivity. None of the samples tested reacted with the MyfA-MIK antigen when antibodies of the IgM and IgA classes were investigated.
75.0% of the Y. enterocolitica WIDAL-positive and blot-positive samples were IgG-positive for the MyfA-MIK antigen. None of these samples reacted with the PsaA-MIK antigen. None of these samples showed IgM or IgA reactivity to the PsaA-MIK or MyfA-MIK antigens.
None of the Yersinia IgG-negative samples (n=19) reacted with the PsaA-MIK antigen. Three of the samples showed isolated anti-MyfA-MIK-IgG reactivity and two of the samples showed isolated anti-PsaA-MIK-IgM reactivity.
Y.
pseudo-
tuberculosis-
Y.
enterocolitica
Yersinia IgG -
The present example provides evidence that, surprisingly, the antigens PsaA or MyfA make it possible to differentiate infections with Y. pseudotuberculosis from infections with Y. enterocolitica, although there are relatively high homologies between the two antigens, which can also lead to cross-reactivities. Cross-reactivities to MyfA-like or PsaA-like antigens, which occur in other enterobacteria, can be ruled out through the use of the other antigens described here, in particular Yop D.
Based on these results it is to be assumed that the device described here could also be used for serologically detecting an infection caused by Y. pestis. However, because a Y. pestis infection—in contrast to a Y. pseudotuberculosis infection—is typically associated with a black, rapidly progressing, symptomatology with a different course (so-called pneumonic plague, bubonic plague), serodiagnosis supported by clinical symptomatology permits reliable differentiation of the two types of infection.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09002105 | Feb 2009 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/051673 | 2/11/2010 | WO | 00 | 8/8/2011 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2010/092093 | 8/19/2010 | WO | A |
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| Number | Date | Country | |
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| 20110306515 A1 | Dec 2011 | US |
