Analysis of the yopA gene encoding the Yop1 virulence determinants of Yersinia spp

Molecular and physiological insights into plague transmission, virulence and etiology

Plague is caused by Yersinia pestis, which evolved from the enteric pathogen Y. pseudotuberculosis, which normally causes a chronic and relatively mild disease. Y. pestis is not only able to parasitize the flea but also highly virulent to rodents and humans, causing epidemics of a systemic and often fatal disease. Y. pestis could be used as a bio-weapon and for bio-terrorism. It uses a number of strategies that allow the pathogen to change its lifestyle rapidly to survive in fleas and to grow in the mammalian hosts. Extensive studies reviewed here give an overall picture of the determinants responsible for plague pathogenesis in mammalians and the transmission by fleas. The availability of multiple genomic sequences and more extensive use of genomics and proteomics technologies should allow a comprehensive dissection of the complex of host-adaptation and virulence in Y. pestis.

Simultaneous display of multiple foreign peptides in the FliD capping and FliC filament proteins of the Escherichia coli flagellum

The bacterial flagellum is composed of more than 20 different proteins. The filament, which constitutes the major extracellular part of the flagellum, is built up of approximately 20,000 FliC molecules that assemble at the growing distal end of the filament. A capping structure composed of five FliD molecules located at the tip of the filament promotes polymerization of FliC. Lack of FliD leads to release of the subunits into the growth medium. We show here that FliD can be successfully used in bacterial surface display. We tested various insertion sites in the capping protein, and the optimal region for display was at the variable region in FliD. Deletion and/or insertion at other sites resulted in decreased formation of flagella. We further developed the technique into a multihybrid display system in which three foreign peptides are simultaneously expressed within the same flagellum, i.e., D repeats of FnBPA from Staphylococcus aureus at the tip and fragments of YadA from Yersinia enterocolitica as well as SlpA from Lactobacillus crispatus along the filament. This technology can have biotechnological applications, e.g., in simultaneous delivery of several effector molecules.

Extrachromosomal DNA of the symbiont Sodalis glossinidius

The extrachromosomal DNA of Sodalis glossinidius from two tsetse fly species was sequenced and contained four circular elements: three plasmids, pSG1 (82 kb), pSG2 (27 kb), and pSG4 (11 kb), and a bacteriophage-like pSG3 (19 kb) element. The information suggests S. glossinidius is evolving towards an obligate association with tsetse flies.

Haemophilus ducreyi Outer membrane determinants, including DsrA, define two clonal populations

The Haemophilus ducreyi outer membrane component DsrA (for ducreyi serum resistance A) is necessary for complete resistance to normal human serum (NHS). When DsrA expression in 19 temporally and geographically diverse clinical isolates of H. ducreyi was examined by Western blotting, 5 of the strains expressed a different immunotype of the DsrA protein (DsrA(II)) than the well-characterized prototypical strain 35000HP (DsrA(I)). The predicted DsrA proteins expressed by the DsrA(II) strains were 100% identical to each other but only 48% identical to that of strain 35000HP. In addition to the DsrA(II) protein, class II strains also expressed variant forms of other outer membrane proteins (OMPs) including NcaA (necessary for collagen adhesion A), DltA (ducreyi lectin A), Hlp (H. ducreyi lipoprotein), major OMP, and/or OmpA2 (for OMP A2) and synthesized a distinct, faster-migrating lipooligosaccharide. Based on these data, strains expressing DsrA(I) were termed class I, and those expressing DsrA(II) were termed class II. Expression of dsrA(II) from strain CIP 542 ATCC in the class I dsrA(I) mutant FX517 (35000HP background), which does not express a DsrA protein, rendered this strain resistant to 50% NHS. This demonstrates that DsrA(II) protein is also critical to serum resistance. Taken together, these results indicate that there are two clonal populations of H. ducreyi. The implications of two classes of H. ducreyi strains differing in important antigenic outer membrane components are discussed.

DNA microarray analysis of genome dynamics in Yersinia pestis: insights into bacterial genome microevolution and niche adaptation

Genomics research provides an unprecedented opportunity for us to probe into the pathogenicity and evolution of the world's most deadly pathogenic bacterium, Yersinia pestis, in minute detail. In our present work, extensive microarray analysis in conjunction with PCR validation revealed that there are considerable genome dynamics, due to gene acquisition and loss, in natural populations of Y. pestis. We established a genomotyping system to group homologous isolates of Y. pestis, based on profiling or gene acquisition and loss in their genomes, and then drew an outline of parallel microevolution of the Y. pestis genome. The acquisition of a number of genomic islands and plasmids most likely induced Y. pestis to evolve rapidly from Yersinia pseudotuberculosis to a new, deadly pathogen. Horizontal gene acquisition also plays a key role in the dramatic evolutionary segregation of Y. pestis lineages (biovars and genomovars). In contrast to selective genome expansion by gene acquisition, genome reduction occurs in Y. pestis through the loss of DNA regions. We also theorized about the links between niche adaptation and genome microevolution. The transmission, colonization, and expansion of Y. pestis in the natural foci of endemic plague are parallel and directional and involve gradual adaptation to the complex of interactions between the environment, the hosts, and the pathogen itself. These adaptations are based on the natural selections against the accumulation of genetic changes within genome. Our data strongly support that the modern plague originated from Yunnan Province in China, due to the arising of biovar orientalis from biovar antiqua rather than mediaevalis.

The Yersinia adhesin YadA collagen-binding domain structure is a novel left-handed parallel beta-roll

The crystal structure of the recombinant collagen-binding domain of Yersinia adhesin YadA from Yersinia enterocolitica serotype O:3 was solved at 1.55 A resolution. The trimeric structure is composed of head and neck regions, and the collagen binding head region is a novel nine-coiled left-handed parallel beta-roll. Before the beta-roll, the polypeptide loops from one monomer to the rest, and after the beta-roll the neck region does the same, making the transition from the globular head region to the narrower stalk domain. This creates an intrinsically stable 'lock nut' structure. The trimeric form of YadA is required for collagen binding, and mutagenesis of its surface residues allowed identification of a putative collagen-binding surface. Furthermore, a new structure-sequence motif for YadA beta-roll was used to identify putative YadA-head-like domains in a variety of human and plant pathogens. Such domains may therefore be a common bacterial strategy for avoiding host response.

Duplex real-time SYBR green PCR assays for detection of 17 species of food- or waterborne pathogens in stools

A duplex real-time SYBR Green LightCycler PCR (LC-PCR) assay with DNA extraction using the QIAamp DNA Stool Mini kit was evaluated with regard to detection of 8 of 17 species of food- or waterborne pathogens in five stool specimens in 2 h or less. The protocol used the same LC-PCR with 20 pairs of specific primers. The products formed were identified based on a melting point temperature (T(m)) curve analysis. The 17 species of food- or waterborne pathogens examined were enteroinvasive Escherichia coli, enteropathogenic E. coli, enterohemorrhagic E. coli, enterotoxigenic E. coli, enteroaggregative E. coli, Salmonella spp., Shigella spp., Yersinia enterocolitica, Yersinia pseudotuberculosis, Campylobacter jejuni, Vibrio cholerae, Vibrio parahaemolyticus, Vibrio vulnificus, Aeromonas spp., Staphylococcus aureus, Clostridium perfringens, and Bacillus cereus. No interference with the LC-PCR assay was observed when stool specimens were artificially inoculated with each bacterial species. The detection levels were approximately 10(5) food- or waterborne pathogenic bacteria per g of stool. The protocol for processing stool specimens for less than 10(4) food- or waterborne pathogenic bacteria per g of stool requires an overnight enrichment step to achieve adequate sensitivity. However, the rapid amplification and reliable detection of specific genes of greater than 10(5) food- or waterborne pathogenic bacteria per g in samples should facilitate the diagnosis and management of food- or waterborne outbreaks.

Molecular genetics, biochemistry and biological role of Yersinia lipopolysaccharide

Lipopolysaccharide (LPS) is the major component of the outer leaflet of the outer membrane of Gram-negative bacteria. The LPS molecule is composed of two biosynthetic entities: the lipid A--core and the O-polysaccharide (O-antigen). Most biological effects of LPS are due to the lipid A part, however, there is an increasing body of evidence also with Yersinia indicating that O-antigen plays an important role in effective colonization of host tissues, resistance to complement-mediated killing and in the resistance to cationic antimicrobial peptides that are key elements of the innate immune system. The biosynthesis of O-antigen requires numerous enzymatic activities and includes the biosynthesis of individual NDP-activated precursor sugars in the cytoplasm, linkage and sugar-specific transferases, O-unit flippase, O-antigen polymerase and O-chain length determinant. Based on this enzymatic mode of O-antigen biosynthesis LPS isolated from bacteria is a heterologous population of molecules; some do not carry any O-antigen while others that do have variation in the O-antigen chain lengths. The genes required for the O-antigen biosynthesis are located in O-antigen gene clusters that in genus Yersinia is located between the hemH and gsk genes. Temperature regulates the O-antigen expression in Y. enterocolitica and Y. pseudotuberculosis; bacteria grown at room temperature (RT, 22-25 degrees C) produce in abundance O-antigen while only trace amounts are present in bacteria grown at 37 degrees C. Even though the amount of O-antigen is known to fluctuate under different growth conditions in many bacteria very little detailed information is available on the control of the O-antigen biosynthetic machinery.

Molecular analysis of transport and oligomerization of the Yersinia enterocolitica adhesin YadA

The Yersinia adhesin YadA is the prototype of a novel class of bacterial adhesins which form oligomeric lollipop-like structures and are anchored in the outer membrane by the C terminus. For YadA, six different regions (R) or domains (D) are predicted from the amino acid sequence: the N-terminal leader sequence, head-D, neck-D, stalk-D, linking-R, and a C-terminal transmembrane region consisting of four beta-strands. To identify structural and functional features of these domains, we performed in-frame deletion mutagenesis and constructed N-terminally tagged YadA variants. Diverse YadA variants were analyzed for outer membrane localization, surface exposure, oligomerization adhesion properties, and ability to protect against complement-mediated lysis. We demonstrated that (i) the C-terminal region (amino acids [aa] 353 to 422) is sufficient for outer membrane insertion and formation of trimers in the outer membrane; (ii) the head, neck, and stalk domains (aa 26 to 330) are surface exposed, forming a passenger domain; and (iii) the linking region (aa 331 to 369) is responsible for outer membrane translocation of the passenger domain. Thus, YadA meets all the criteria of an autotransporter. The same may be true for all other members of the YadA family, forming a subfamily of surface-attached oligomeric autotransporters. Moreover, in-frame truncation mutagenesis suggested that the head and neck domains together form the YadA-binding module which is located on the top of the stalk. However, the YadA-binding module did not confer serum resistance. Mutants lacking the head and neck domain were resistant to complement-mediated lysis. In-frame truncation of the stalk domain did not result in significant attenuation of the mutant in an orogastric mouse infection model.

PCR detection of virulence genes in Yersinia enterocolitica and Yersinia pseudotuberculosis and investigation of virulence gene distribution

PCR-based assays were developed for the detection of plasmid- and chromosome-borne virulence genes in Yersinia enterocolitica and Yersinia pseudotuberculosis, to investigate the distribution of these genes in isolates from various sources. The results of PCR genotyping, based on 5 virulence-associated genes of 140 strains of Y. enterocolitica, were compared to phenotypic tests, such as biotyping and serotyping, and to virulence plasmid-associated properties such as calcium-dependent growth at 37 degrees C and Congo red uptake. The specificity of the PCR results was validated by hybridization. Genotyping data correlated well with biotype data, and most biotypes resulted in (nearly) homogeneous genotypes for the chromosomal virulence genes (ystA, ystB, and ail); however, plasmid-borne genes (yadA and virF) were detected with variable efficiency, due to heterogeneity within the bacterial population for the presence of the virulence plasmid. Of the virulence genes, only ystB was present in biotype 1A; however, within this biotype, pathogenic and apathogenic isolates could not be distinguished based on the detection of virulence genes. Forty Y. pseudotuberculosis isolates were tested by PCR for the presence of inv, yadA, and lcrF. All isolates were inv positive, and 88% of the isolates contained the virulence plasmid genes yadA and lcrF. In conclusion, this study shows that genotyping of Yersinia spp., based on both chromosome- and plasmid-borne virulence genes, is feasible and informative and can provide a rapid and reliable genotypic characterization of field isolates.

Occurrence of Yersinia enterocolitica and Campylobacter spp. in slaughter pigs and consequences for meat inspection, slaughtering, and dressing procedures

The purpose of the present investigation was to assess the occurrence of Yersinia enterocolitica and Campylobacter spp. in the lymphoid tissues and intestinal tract in pigs and the risk for contamination during the compulsory meat inspection procedures and the procedures during slaughtering and dressing. Another objective of the investigation was to compare traditional isolation methods, the use of a polymerase chain reaction (PCR) method (BUGS'n BEADS bacterial DNA isolation kit) and an ELISA method (VIDAS CAM) as tools in risk management in the slaughterhouse. The results indicate that the compulsory procedure for the incision of the submaxillary lymph nodes represents a cross-contamination risk for virulent Yersinia. In the screening of 97 animals in 1999, 5.2% of the samples were positive, and by the sampling of 24 samples in 2000-2001, 12.5% of the samples were positive. In the last case, Y. enterocolitica O:3 was found in the kidney region in one of the subsequent carcasses that was only touched by the meat inspection personnel before sampling. In addition, incision of the mesenteric lymph nodes might represent a cross-contamination risk since 8.3% of the samples were positive. The association between antibody titres and the occurrence of virulent yersiniae in the tonsils (21-18) was striking, with virulent yersiniae found in the tonsils in most pigs with high titres. The contents of the stomach, ileum, caecum, and colon also represent contamination risks for Y. enterocolitica O:3 if the slaughterhouse personnel cuts into the viscera with their knives by accident; the frequency of virulent Yersinia varied from 4.2% to 16.7% within these sections. Campylobacter was detected in the gastrointestinal tract of all pigs, and the high contamination of tonsils (66.7%) and intestinal tract (100%) might represent an occupational health hazard. There was no statistical difference between the traditional method for isolation of Y. enterocolitica [International Organization for Standardization, 1994. Microbiology-General Guidance for the Detection of Presumptive Pathogenic Yersinia enterocolitica (ISO 10273). International Organization for Standardization, Genève, Switzerland (16 pp.)] and the BUGS'n BEADS detection method for virulent Y. enterocolitica. Likewise, there was no statistical difference between the traditional method for isolation of Campylobacter spp. [Nordic Committee on Food Analysis, 1990. Campylobacter jejuni/coli. Detection in Food. Method No. 119, 2nd ed. Nordic Committee on Food Analysis, Esbo (7 pp.)] and the BUGS'n BEADS detection method or the VIDAS CAM method for detection of Campylobacter spp.

Activation of prophage eib genes for immunoglobulin-binding proteins by genes from the IbrAB genetic island of Escherichia coli ECOR-9

Four distinct Escherichia coli immunoglobulin-binding (eib) genes, each of which encodes a surface-exposed protein that binds immunoglobulins in a nonimmune manner, are carried by separate prophages in E. coli reference (ECOR) strain ECOR-9. Each eib gene was transferred to test E. coli strains, both in the form of multicopy recombinant plasmids and as lysogenized prophage. The derived lysogens express little or no Eib protein, in sharp contrast to the parental lysogen, suggesting that ECOR-9 has an expression-enhancing activity that the derived lysogens lack. Supporting this hypothesis, we cloned from ECOR-9 overlapping genes, ibrA and ibrB (designation is derived from "immunoglobulin-binding regulator"), which together activated eib expression in the derived lysogens. The proteins encoded by ibrA and ibrB are very similar to uncharacterized proteins encoded by genes of Salmonella enterica serovar Typhi and E. coli O157:H7 (in a prophage-like element of the Sakai strain and in two O islands of strain EDL933). The genomic segment containing ibrA and ibrB has been designated the IbrAB island. It contains regions of homology to the Shiga toxin-converting prophage, Stx2, as well as genes homologous to phage antirepressor genes. The left boundary between the IbrAB island and the chromosomal framework is located near min 35.8 of the E. coli K-12 genome. Homology to IbrAB was found in certain other ECOR strains, including the other five eib-positive strains and most strains of the phylogenetic group B2. Sequencing of a 1.1-kb portion of ibrAB revealed that the other eib-positive strains diverge by </=0.1% from ECOR-9, whereas eib-negative ECOR-47 diverges by 16%.

NadA, a novel vaccine candidate of Neisseria meningitidis

Neisseria meningitidis is a human pathogen, which, in spite of antibiotic therapy, is still a major cause of mortality due to sepsis and meningitis. Here we describe NadA, a novel surface antigen of N. meningitidis that is present in 52 out of 53 strains of hypervirulent lineages electrophoretic types (ET) ET37, ET5, and cluster A4. The gene is absent in the hypervirulent lineage III, in N. gonorrhoeae and in the commensal species N. lactamica and N. cinerea. The guanine/cytosine content, lower than the chromosome, suggests acquisition by horizontal gene transfer and subsequent limited evolution to generate three well-conserved alleles. NadA has a predicted molecular structure strikingly similar to a novel class of adhesins (YadA and UspA2), forms high molecular weight oligomers, and binds to epithelial cells in vitro supporting the hypothesis that NadA is important for host cell interaction. NadA induces strong bactericidal antibodies and is protective in the infant rat model suggesting that this protein may represent a novel antigen for a vaccine able to control meningococcal disease caused by three hypervirulent lineages.

Nonimmune binding of human immunoglobulin A (IgA) and IgG Fc by distinct sequence segments of the EibF cell surface protein of Escherichia coli

The eib genes of Escherichia coli encode surface-exposed proteins which bind immunoglobulins (Ig) such as the Fc fragment of human IgG (IgG Fc) in a nonimmune manner. The Eib proteins belong to a family which includes YadA of Yersinia, UspA2 of Moraxella, and DsrA of Haemophilus ducreyi. This family of surface-exposed proteins shares several features, such as the ability to impart resistance to human serum complement and a tendency to exist as stable multimers. Four genes, eibA, eibC, eibD and eibE, were previously identified and cloned from ECOR-9, a strain from the E. coli reference collection. EibC, -D, and -E bind human serum IgA in addition to IgG, but no IgA binding has been observed for EibA. Here, we report the cloning of a new eib gene, eibF, from a second strain of E. coli, ECOR-2. The product, EibF, has a relatively strong preference for IgA. Like the other eib genes, eibF attenuates serum sensitivity, occurs as a stable multimer, and is associated with a prophage. By subcloning portions of the eibA and eibF genes, we have identified distinct sequence segments sufficient to cause Ig binding, multimerization, and discrimination between IgA and IgG. The ability to multimerize is associated with a sequence close to the C terminus that is homologous to other family members such as YadA. Binding of IgG Fc is associated with a sequence that is highly conserved among all Eib proteins but otherwise unique. Binding of IgA is associated with a sequence of EibF that is not similar to any EibA sequence.

Comparison of culture, multiplex, and 5' nuclease polymerase chain reaction assays for the rapid detection of Yersinia enterocolitica in swine and pork products

Bacteriological culture was compared with multiplex and fluorogenic (TaqMan) polymerase chain reaction (PCR) assays for the detection of attachment invasion locus (ail)-bearing Yersinia enterocolitica in market weight swine, chitterlings, and ground pork. The TaqMan assay detected 1 pg of purified Y. enterocolitica DNA, whereas conventional gel-based PCR detected I ng of the same. The presence of ail-bearing Y. enterocolitica was tested in pork and feces artificially inoculated with Y. enterocolitica strain NADC 5561. The sensitivity limits of culture, multiplex, and TaqMan PCR assays were 4 x 10(3), 4 x 10(2), and 0.4 CFU/g, respectively, for the artificially inoculated pork. The sensitivity limits were 4 x 10(2), 4 x 10(2), and 0.4 CFU/g, respectively, for feces after a 48-h enrichment in a Yersinia selective broth. By the culture method, Y. enterocolitica was not detected in any of the swine specimens (n = 2,403) examined. By contrast, it was detected in 48 (2%) of the swine samples screened using the multiplex PCR and in 656 (27.2%) of these samples using the TaqMan assay. Using the culture method, Y. enterocolitica was detected in 8% of chitterling samples (n = 350) and in none of the ground pork samples (n = 350). It was identified in 27% of the chitterling samples using multiplex PCR and in 79% of these samples using the TaqMan assay. Ten percent of the ground pork samples contained Y. enterocolitica, as determined by the multiplex PCR, and 38% based on the TaqMan assay. The results suggest that pork products harbor more ail-bearing Y. enterocolitica than selected organs of freshly slaughtered hogs and that the TaqMan assay is more sensitive than either the multiplex PCR or traditional culture methods.

The Pla surface protease/adhesin of Yersinia pestis mediates bacterial invasion into human endothelial cells

The plasminogen activator Pla of Yersinia pestis belongs to the omptin family of enterobacterial surface proteases and is responsible for the highly efficient invasion of the plague bacterium from the subcutaneous infection site into the circulation. Y. pestis has been reported to invade human epithelial cells. Here, we investigated the role of Pla in bacterial invasion into human endothelial cells. Expression of Pla in recombinant Escherichia coli XL1(pMRK1) enhanced bacterial invasion into ECV304 cells. The invasiveness was not affected by substitution mutation at the residues S99 or D206 that are needed for the proteolytic activity of Pla. Pla-expressing bacteria adhered to the extracellular matrix of ECV304 cells. Only weak adhesion and poor invasion were seen with the recombinant E. coli XL1(pMRK2), which expresses the omptin homolog from E. coli. The results identify Pla as an invasion protein of Y. pestis and show that the invasive function does not involve the proteolytic activity of Pla.

Protein regions important for plasminogen activation and inactivation of alpha2-antiplasmin in the surface protease Pla of Yersinia pestis

The plasminogen activator, surface protease Pla, of the plague bacterium Yersinia pestis is an important virulence factor that enables the spread of Y. pestis from subcutaneous sites into circulation. Pla-expressing Y. pestis and recombinant Escherichia coli formed active plasmin in the presence of the major human plasmin inhibitor, alpha2-antiplasmin, and the bacteria were found to inactivate alpha2-antiplasmin. In contrast, only poor plasminogen activation and no cleavage of alpha2-antiplasmin was observed with recombinant bacteria expressing the homologous gene ompT from E. coli. A beta-barrel topology model for Pla and OmpT predicted 10 transmembrane beta-strands and five surface-exposed loops L1-L5. Hybrid Pla-OmpT proteins were created by substituting each of the loops between Pla and OmpT. Analysis of the hybrid molecules suggested a critical role of L3 and L4 in the substrate specificity of Pla towards plasminogen and alpha2-antiplasmin. Substitution analysis at 25 surface-located residues showed the importance of the conserved residues H101, H208, D84, D86, D206 and S99 for the proteolytic activity of Pla-expressing recombinant E. coli. The mature alpha-Pla of 292 amino acids was processed into beta-Pla by an autoprocessing cleavage at residue K262, and residues important for the self-recognition of Pla were identified. Prevention of autoprocessing of Pla, however, had no detectable effect on plasminogen activation or cleavage of alpha2-antiplasmin. Cleavage of alpha2-antiplasmin and plasminogen activation were influenced by residue R211 in L4 as well as by unidentified residues in L3. OmpT, which is not associated with invasive bacterial disease, was converted into a Pla-like protease by deleting residues D214 and P215, by substituting residue K217 for R217 in L4 of OmpT and also by substituting the entire L3 with that from Pla. This simple modification of the surface loops and the substrate specificity of OmpT exemplifies the evolution of a housekeeping protein into a virulence factor by subtle mutations at critical protein regions. We propose that inactivation of alpha2-antiplasmin by Pla of Y. pestis promotes uncontrolled proteolysis and contributes to the invasive character of plague.

Pseudogenes, junk DNA, and the dynamics of Rickettsia genomes

Studies of neutrally evolving sequences suggest that differences in eukaryotic genome sizes result from different rates of DNA loss. However, very few pseudogenes have been identified in microbial species, and the processes whereby genes and genomes deteriorate in bacteria remain largely unresolved. The typhus-causing agent, Rickettsia prowazekii, is exceptional in that as much as 24% of its 1.1-Mb genome consists of noncoding DNA and pseudogenes. To test the hypothesis that the noncoding DNA in the R. prowazekii genome represents degraded remnants of ancestral genes, we systematically examined all of the identified pseudogenes and their flanking sequences in three additional Rickettsia species. Consistent with the hypothesis, we observe sequence similarities between genes and pseudogenes in one species and intergenic DNA in another species. We show that the frequencies and average sizes of deletions are larger than insertions in neutrally evolving pseudogene sequences. Our results suggest that inactivated genetic material in the Rickettsia genomes deteriorates spontaneously due to a mutation bias for deletions and that the noncoding sequences represent DNA in the final stages of this degenerative process.

Structure and sequence analysis of Yersinia YadA and Moraxella UspAs reveal a novel class of adhesins

The non-fimbrial adhesins, YadA of enteropathogenic Yersinia species, and UspA1 and UspA2 of Moraxella catarrhalis, are established pathogenicity factors. In electron micrographs, both surface proteins appear as distinct 'lollipop'-shaped structures forming a novel type of surface projection on the outer membranes. These structures, amino acid sequence analysis of these molecules and yadA gene manipulation suggest a tripartite organization: an N-terminal oval head domain is followed by a putative coiled-coil rod and terminated by a C-terminal membrane anchor domain. In YadA, the head domain is involved in autoagglutination and binding to host cells and collagen. Analysis of the coiled-coil segment of YadA revealed unusual pentadecad repeats with a periodicity of 3.75, which differs significantly from the 3.5 periodicity found in the Moraxella UspAs and other canonical coiled coils. These findings predict that the surface projections are formed by oligomers containing right- (Yersinia) or left-handed (Moraxella) coiled coils. Strikingly, sequence comparison revealed that related proteins are found in many proteobacteria, both human pathogenic and environmental species, suggesting a common role in adaptation to specific ecological niches.

Rapid 5' nuclease (TaqMan) assay for detection of virulent strains of Yersinia enterocolitica

We have developed a rapid procedure for the detection of virulent Yersinia enterocolitica in ground pork by combining a previously described PCR with fluorescent dye technologies. The detection method, known as the fluorogenic 5' nuclease assay (TaqMan), produces results by measuring the fluorescence produced during PCR amplification, requiring no post-PCR processing. The specificity of the chromosomal yst gene-based assay was tested with 28 bacterial isolates that included 7 pathogenic and 7 nonpathogenic serotypes of Y. enterocolitica, other species of Yersinia (Y. aldovae, Y. pseudotuberculosis, Y. mollaretti, Y. intermedia, Y. bercovieri, Y. ruckeri, Y. frederiksenii, and Y. kristensenii), and other enteric bacteria (Escherichia, Salmonella, Citrobacter, and Flavobacterium). The assay was 100% specific in identifying the pathogenic strains of Y. enterocolitica. The sensitivity of the assay was found to be >/=10(2) CFU/ml in pure cultures and >/=10(3) CFU/g in spiked ground pork samples. Results of the assay with food enrichments prespiked with Y. enterocolitica serotypes O:3 and O:9 were comparable to standard culture results. Of the 100 field samples (ground pork) tested, 35 were positive for virulent Y. enterocolitica with both 5' nuclease assay and conventional virulence tests. After overnight enrichment the entire assay, including DNA extraction, amplification, and detection, could be completed within 5 h.

Characterization of the O-antigen gene clusters of Yersinia pseudotuberculosis and the cryptic O-antigen gene cluster of Yersinia pestis shows that the plague bacillus is most closely related to and has evolved from Y. pseudotuberculosis serotype O:1b

One of the most virulent and feared bacterial pathogens is Yersinia pestis, the aetiologic agent of bubonic plague. Characterization of the O-antigen gene clusters of 21 serotypes of Yersinia pseudotuberculosis and the cryptic O-antigen gene cluster of Y. pestis showed that the plague bacillus is most closely related to and has evolved from Y. pseudotuberculosis serotype O:1b. The nucleotide sequences of both gene clusters (about 20.5 kb each) were determined and compared to identify the differences that caused the silencing of the Y. pestis gene cluster. At the nucleotide sequence level, the loci were 98.9% identical and, of the 17 biosynthetic genes identified from the O:1b gene cluster, five were inactivated in the Y. pestis cluster, four by insertions or deletions of one nucleotide and one by a deletion of 62 nucleotides. Apparently, the expression of the O-antigen is not beneficial for the virulence or to the lifestyle of Y. pestis and, therefore, as one step in the evolution of Y. pestis, the O-antigen gene cluster was inactivated.

Functional mapping of the Yersinia enterocolitica adhesin YadA. Identification Of eight NSVAIG - S motifs in the amino-terminal half of the protein involved in collagen binding

The virulence plasmid-encoded YadA of Yersinia enterocolitica serotype O:3 is a 430-amino-acid outer membrane protein, synthesized with a 25-amino-acid signal peptide. YadA forms homotrimeric surface structures that function as adhesin between bacteria and collagen as well as other host proteins. The structure-function relationships of YadA were studied, and the collagen-binding determinants of YadA were located to its amino-terminal half. Collagen did not bind to any of the overlapping 16-mer YadA peptides, indicating that the collagen binding site of YadA is conformational. Epitope mapping of YadA identified 12 linear antigenic epitopes altogether. Seven epitopes were uniquely recognized by an anti-YadA antiserum able to inhibit collagen binding. Four of these epitopes shared a motif NSVAIG-S that is repeated eight times within the N-terminal half of YadA. Site-directed mutagenesis showed that these motifs are absolutely required for YadA-mediated collagen binding, revealing a novel type of collagen-binding mechanism.

Evaluation of a Yersinia adhesion gene (yadA) specific PCR for the identification of enteropathogenic Yersinia enterocolitica

A total of 101 Yersinia enterocolitica strains was investigated with a PCR assay [Blais and Phillipe, Food Control, 6 (1995) 211-214] targeting the Yersinia adhesin gene (yadA) responsible for autoagglutination. Compared to the autoagglutination test the PCR assay has a specificity of 100% but a sensitivity of only 70%. This failure might be caused by the sequence heterogeneity of yadA.

Four different genes responsible for nonimmune immunoglobulin-binding activities within a single strain of Escherichia coli

Certain Escherichia coli strains bind the Fc fragment of immunoglobulin G (IgG) at the bacterial cell surface. Previous work established that this nonimmune Ig binding depends on several large proteins with apparent molecular masses that can exceed 200 kDa. For E. coli strain ECOR-9, four distinct genes (designated eibA, eibC, eibD, and eibE) are responsible for Ig binding. Two eib genes are linked to eaa genes, which are homologous to genes for the autotransporter family of secreted proteins. With reference to the E. coli K-12 chromosome, the eibA-eaaA cluster is adjacent to trpA (min 28.3) while the eibC-eaaC cluster is adjacent to aspS (min 42. 0). Sequence adjacent to the eibA-eaaA cluster converges with that of strain K-12 precisely as observed for the Atlas family of prophages, suggesting that eibA is part of one of these. All four eib genes, when cloned into plasmid vectors, impart IgG binding to E. coli K-12 strains, and three impart IgA binding also. The IgG binding occurs at the bacterial cell surface, and its expression increases survival in serum by up to 3 orders of magnitude. The eib sequences predict a C-terminal peptide motif that is characteristic of outer membrane proteins, and the protein sequences show significant similarity near the C terminus to both the YadA virulence factor of Yersinia species and the universal surface protein A II of Moraxella catarrhalis. The sizes predicted for Eib proteins from DNA sequence are much smaller than their apparent sizes on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, possibly reflecting stable oligomerization.

Serum resistance in Haemophilus ducreyi requires outer membrane protein DsrA

Haemophilus ducreyi is resistant to killing by normal serum antibody and complement. We discovered an H. ducreyi outer membrane protein required for expression of serum resistance and termed it DsrA (for "ducreyi serum resistance A"). The dsrA locus was cloned, sequenced, and mutagenized. An isogenic mutant (FX517) of parent strain 35000 was constructed and characterized, and it was found to no longer express dsrA. FX517 was at least 10-fold more serum susceptible than 35000. DsrA was expressed by all strains of H. ducreyi tested, except three naturally occurring, avirulent, serum-sensitive strains. FX517 and the three naturally occurring dsrA-nonexpressing strains were complemented in trans with a plasmid expressing dsrA. All four strains were converted to a serum-resistant phenotype, including two that contained truncated lipooligosaccharide (LOS). Therefore, serum resistance in H. ducreyi does not require expression of full-length LOS but does require expression of dsrA. The dsrA locus from eight additional H. ducreyi strains was sequenced, and the deduced amino acid sequences were more than 85% identical. The major difference between the DsrA proteins was due to the presence of one, two, or three copies of the heptameric amino acid repeat NTHNINK. These repeats account for the variability in apparent molecular mass of the monomeric form of DsrA (28 to 35 kDa) observed in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Since DsrA is present in virulent strains, is highly conserved, and is required for serum resistance, we speculate that it may be a virulence factor and a potential vaccine candidate.

Yersinia pestis, the cause of plague, is a recently emerged clone of Yersinia pseudotuberculosis

Plague, one of the most devastating diseases of human history, is caused by Yersinia pestis. In this study, we analyzed the population genetic structure of Y. pestis and the two other pathogenic Yersinia species, Y. pseudotuberculosis and Y. enterocolitica. Fragments of five housekeeping genes and a gene involved in the synthesis of lipopolysaccharide were sequenced from 36 strains representing the global diversity of Y. pestis and from 12-13 strains from each of the other species. No sequence diversity was found in any Y. pestis gene, and these alleles were identical or nearly identical to alleles from Y. pseudotuberculosis. Thus, Y. pestis is a clone that evolved from Y. pseudotuberculosis 1,500-20,000 years ago, shortly before the first known pandemics of human plague. Three biovars (Antiqua, Medievalis, and Orientalis) have been distinguished by microbiologists within the Y. pestis clone. These biovars form distinct branches of a phylogenetic tree based on restriction fragment length polymorphisms of the locations of the IS100 insertion element. These data are consistent with previous inferences that Antiqua caused a plague pandemic in the sixth century, Medievalis caused the Black Death and subsequent epidemics during the second pandemic wave, and Orientalis caused the current plague pandemic.

The 102-kilobase pgm locus of Yersinia pestis: sequence analysis and comparison of selected regions among different Yersinia pestis and Yersinia pseudotuberculosis strains

We report the complete 119,443-bp sequence of the pgm locus from Yersinia pestis and its flanking regions. Sequence analysis confirms that the 102-kb unstable pgm locus is composed of two distinct parts: the pigmentation segment and a high-pathogenicity island (HPI) which carries virulence genes involved in iron acquisition (yersiniabactin biosynthetic gene cluster). Within the HPI, three genes coding for proteins related to phage proteins were uncovered. They are located at both extremities indicating that the entire HPI was acquired en bloc by phage-mediated horizontal transfer. We identified, within the pigmentation segment, two novel loci that may be involved in virulence: a fimbriae gene cluster and a locus probably encoding a two component regulatory system similar to the BvgAS regulatory system of Bordetella pertussis. Three genes containing frameshift mutations and two genes interrupted by insertion element insertion were found within this region. To investigate diversity among different Y. pestis and Yersinia pseudotuberculosis strains, the sequence of selected regions of the pgm locus and flanking regions were compared from 20 different Y. pestis and 10 Y. pseudotuberculosis strains. The results showed that the genes interrupted in Y. pestis are intact in Y. pseudotuberculosis. However, one of these mutations, in the bvgS homologue, is only present in Y. pestis strains of biovar Orientalis and not in those of the biovars Antiqua and Medievalis. The results obtained by analysis of variable positions in the sequence are in accordance with historical records, confirming that biovar Orientalis is the most recent lineage. Furthermore, sequence comparisons among 29 Yersinia strains suggest that Y. pestis is a recently emerged pathogen that is probably entering the initial phase of reductive evolution.

Characterization of the Moraxella catarrhalis uspA1 and uspA2 genes and their encoded products

The uspA1 and uspA2 genes of M. catarrhalis O35E encode two different surface-exposed proteins which were previously shown to share a 140-amino-acid region with 93% identity (C. Aebi, I. Maciver, J. L. Latimer, L. D. Cope, M. K. Stevens, S. E. Thomas, G. H. McCracken, Jr., and E. J. Hansen, Infect. Immun. 65:4367-4377, 1997). The N-terminal amino acid sequences of the mature forms of both UspA1 and UspA2 from strain O35E were determined after enzymatic treatment to remove the N-terminal pyroglutamyl residue that had blocked Edman degradation. Mass spectrometric analysis indicated that the molecular mass of UspA1 from M. catarrhalis O35E was 83,500 +/- 116 Da. Nucleotide sequence analysis of the uspA1 and uspA2 genes from three other M. catarrhalis strains (TTA24, ATCC 25238, and V1171) revealed that the encoded protein products were very similar to those from strain O35E. Western blot analysis was used to confirm that each of these three strains of M. catarrhalis expressed both UspA1 and UspA2 proteins. Several different and repetitive amino acid motifs were present in both UspA1 and UspA2 from these four strains, and some of these were predicted to form coiled coils. Linear DNA templates were used in an in vitro transcription-translation system to determine the sizes of the monomeric forms of the UspA1 and UspA2 proteins from strains O35E and TTA24.

The tranquilizing injection of Yersinia proteins: a pathogen's strategy to resist host defense

Pathogenic bacteria of the genus Yersinia possess a type III secretion apparatus by which they can inject up to six effector proteins into host cells. These so-called effector Yops (Yersinia outer proteins) disrupt cellular immune defense functions such as TNF-alpha release, O2-production or phagocytosis and thereby allow Yersinia to grow extracellularly. Recent findings indicate that the effector Yops are highly active proteins that engage in crucial eukaryotic signaling mechanisms. For instance, the translocated tyrosine phosphatase YopH dephosphorylates the focal adhesion proteins paxillin and p130Cas within target cells. Furthermore, the Yersinia effector YopP is able to induce apoptosis in macrophages presumably by blocking MAP kinase and NFKB mediated signaling events. Here we discuss recent advances concerning the intracellular targets and biochemical signaling mechanisms regulated by the translocated Yersinia effectors.

Detection of pathogenic Yersinia enterocolitica in enrichment media and pork by a multiplex PCR: a study of sample preparation and PCR-inhibitory components

A multiplex PCR assay including sample preparation was developed to detect viable pathogenic strains of Yersinia enterocolitica in PCR-inhibitory samples, such as pork and enrichment media. The method developed was used to simultaneously detect the plasmid-borne virulence gene yadA and a Yersinia-specific region of the 16S rRNA gene. According to an auto-agglutination test for virulence-plasmid-bearing strains of Y. enterocolitica, all potential pathogenic strains tested were detected by the assay. A DNA extraction procedure, an aqueous two-phase system composed of polyethylene glycol 4000 and dextran 40 and a buoyant density centrifugation method, based on Percoll, were compared with regard to their efficiency in separating Yersinia enterocolitica from PCR inhibitors originating from enrichment media and pork. Using the density gradient centrifugation method resulted in a detection level of 4.0 x 10(2) CFU Y. enterocolitica per ml enrichment media. To ensure detection of viable bacteria a short enrichment step was included in the sample preparation together with the density gradient centrifugation. When this sample treatment method was evaluated with a selective enrichment medium together with a background flora inoculated with approximately 1.0 x 10(1) CFU per ml of Y. enterocolitica and incubated at 25 degrees C, a positive PCR result was obtained after 6 to 8 h. Our results indicate that selective enrichment followed by buoyant density gradient centrifugation provides a convenient and user-friendly sample preparation method prior to PCR.

The virulence plasmid of Yersinia, an antihost genome

The 70-kb virulence plasmid enables Yersinia spp. (Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica) to survive and multiply in the lymphoid tissues of their host. It encodes the Yop virulon, an integrated system allowing extracellular bacteria to disarm the cells involved in the immune response, to disrupt their communications, or even to induce their apoptosis by the injection of bacterial effector proteins. This system consists of the Yop proteins and their dedicated type III secretion apparatus, called Ysc. The Ysc apparatus is composed of some 25 proteins including a secretin. Most of the Yops fall into two groups. Some of them are the intracellular effectors (YopE, YopH, YpkA/YopO, YopP/YopJ, YopM, and YopT), while the others (YopB, YopD, and LcrV) form the translocation apparatus that is deployed at the bacterial surface to deliver the effectors into the eukaryotic cells, across their plasma membrane. Yop secretion is triggered by contact with eukaryotic cells and controlled by proteins of the virulon including YopN, TyeA, and LcrG, which are thought to form a plug complex closing the bacterial secretion channel. The proper operation of the system also requires small individual chaperones, called the Syc proteins, in the bacterial cytosol. Transcription of the genes is controlled both by temperature and by the activity of the secretion apparatus. The virulence plasmid of Y. enterocolitica and Y. pseudotuberculosis also encodes the adhesin YadA. The virulence plasmid contains some evolutionary remnants including, in Y. enterocolitica, an operon encoding resistance to arsenic compounds.

Expression of plasminogen activator pla of Yersinia pestis enhances bacterial attachment to the mammalian extracellular matrix

The effect of the plasminogen activator Pla of Yersinia pestis on the adhesiveness of bacteria to the mammalian extracellular matrix was determined. Y. pestis KIM D27 harbors the 9.5-kb plasmid pPCP1, encoding Pla and pesticin; the strain efficiently adhered to the reconstituted basement membrane preparation Matrigel, to the extracellular matrix prepared from human lung NCI-H292 epithelial cells, as well as to immobilized laminin. The isogenic strain Y. pestis KIM D34 lacking pPCP1 exhibited lower adhesiveness to both matrix preparations and to laminin. Both strains showed weak adherence to type I, IV, and V collagens as well as to human plasma and cellular fibronectin. The Pla-expressing recombinant Escherichia coli LE392(pC4006) exhibited specific adhesiveness to both extracellular matrix preparations as well as to laminin. The Pla-expressing strains showed a low-affinity adherence to another basement membrane component, heparan sulfate proteoglycan, but not to chondroitin sulfate proteoglycan. The degradation of radiolabeled laminin, heparan sulfate proteoglycan, or human lung extracellular matrix by the Pla-expressing recombinant E. coli required the presence of plasminogen, and degradation was inhibited by the plasmin inhibitors aprotinin and alpha2-antiplasmin. Our results indicate a function of Pla in enhancing bacterial adhesion to extracellular matrices. Y. pestis also exhibits a low level of Pla-independent adhesiveness to extracellular matrices.

DNA sequencing and analysis of the low-Ca2+-response plasmid pCD1 of Yersinia pestis KIM5

The low-Ca2+-response (LCR) plasmid pCD1 of the plague agent Yersinia pestis KIM5 was sequenced and analyzed for its genetic structure. pCD1 (70,509 bp) has an IncFIIA-like replicon and a SopABC-like partition region. We have assigned 60 apparently intact open reading frames (ORFs) that are not contained within transposable elements. Of these, 47 are proven or possible members of the LCR, a major virulence property of human-pathogenic Yersinia spp., that had been identified previously in one or more of Y. pestis or the enteropathogenic yersiniae Yersinia enterocolitica and Yersinia pseudotuberculosis. Of these 47 LCR-related ORFs, 35 constitute a continuous LCR cluster. The other LCR-related ORFs are interspersed among three intact insertion sequence (IS) elements (IS100 and two new IS elements, IS1616 and IS1617) and numerous defective or partial transposable elements. Regional variations in percent GC content and among ORFs encoding effector proteins of the LCR are additional evidence of a complex history for this plasmid. Our analysis suggested the possible addition of a new Syc- and Yop-encoding operon to the LCR-related pCD1 genes and gave no support for the existence of YopL. YadA likely is not expressed, as was the case for Y. pestis EV76, and the gene for the lipoprotein YlpA found in Y. enterocolitica likely is a pseudogene in Y. pestis. The yopM gene is longer than previously thought (by a sequence encoding two leucine-rich repeats), the ORF upstream of ypkA-yopJ is discussed as a potential Syc gene, and a previously undescribed ORF downstream of yopE was identified as being potentially significant. Eight other ORFs not associated with IS elements were identified and deserve future investigation into their functions.

Structural organization of virulence-associated plasmids of Yersinia pestis

The complete nucleotide sequence and gene organization of the three virulence plasmids from Yersinia pestis KIM5 were determined. Plasmid pPCP1 (9,610 bp) has a GC content of 45.3% and encodes two previously known virulence factors, an associated protein, and a single copy of IS100. Plasmid pCD1 (70,504 bp) has a GC content of 44.8%. It is known to encode a number of essential virulence determinants, regulatory functions, and a multiprotein secretory system comprising the low-calcium response stimulation that is shared with the other two Yersinia species pathogenic for humans (Y. pseudotuberculosis and Y. enterocolitica). A new pseudogene, which occurs as an intact gene in the Y. enterocolitica and Y. pseudotuberculosis-derived analogues, was found in pCD1. It corresponds to that encoding the lipoprotein YlpA. Several intact and partial insertion sequences and/or transposons were also found in pCD1, as well as six putative structural genes with high homology to proteins of unknown function in other yersiniae. The sequences of the genes involved in the replication of pCD1 are highly homologous to those of the cognate plasmids in Y. pseudotuberculosis and Y. enterocolitica, but their localization within the plasmid differs markedly from those of the latter. Plasmid pMT1 (100,984 bp) has a GC content of 50.2%. It possesses two copies of IS100, which are located 25 kb apart and in opposite orientations. Adjacent to one of these IS100 inserts is a partial copy of IS285. A single copy of an IS200-like element (recently named IS1541) was also located in pMT1. In addition to 5 previously described genes, such as murine toxin, capsule antigen, capsule anchoring protein, etc., 30 homologues to genes of several bacterial species were found in this plasmid, and another 44 open reading frames without homology to any known or hypothetical protein in the databases were predicted.

Examination of Serpulina pilosicoli for attachment and invasion determinants of Enterobacteria

The spirochaete, Serpulina pilosicoli, is the agent of intestinal spirochaetosis, a diarrhoeal disease of humans and other species. By mechanisms as yet unknown, large numbers of these spirochaetes intimately attach to the colonic mucosa by one cell end. In some infected individuals, the spirochaetes may invade the lamina propria and adjacent tissues, and they may cause spirochaetaemia. To examine S. pilosicoli for pathogenic determinants homologous with Enterobacteria, DNA was extracted from six strains of S. pilosicoli and hybridised at low stringency with DNA probes derived from the inv, ail and yadA genes of Yersinia enterocolitica, the eae gene from enteropathogenic Escherichia coli and a probe derived from the virulence plasmid of Shigella flexneri. No hybridisation of the enterobacterial probes to S. pilosicoli DNA was detected, indicating that these gene sequences, which are known to be involved in the attachment and invasion processes of the other intestinal pathogens, were not present in the spirochaetes.

Identification of PhoP-PhoQ activated genes within a duplicated region of the Salmonella typhimurium chromosome

Salmonellae virulence requires the PhoP-PhoQ two-component regulatory system. PhoP-PhoQ activate the transcription of genes following phagocytosis by macrophages which are necessary for survival within the phagosome environment. Thirteen previously undefined PhoP-activated gene fusions generated by MudJ and TnphoA (pag A, and E-P, respectively) were cloned and sequenced. Most pag products show no similarity to proteins in the database, while others are predicted to encode: a UDP-glucose dehydrogenase (pagA); a protein with similarity to the product of an E. coli aluminium-induced gene (pagH); a protein encoded within a Salmonella-unique region adjacent to the sinR gene (pagN); a protein similar to a product of the Yersinia virulence plasmid (pagO); and a protein with similarity to CrcA which is necessary for resistance of E. coli to camphor (pagP). Of the pag characterized, only pagK, M and O were closely linked. pagJ and pagK were shown to be unlinked but nearly identical in DNA sequence, as each was located within a 1.6 kb DNA duplication. The translations of sequences surrounding pagJ and pagK show similarity to proteins from extrachromosomal elements as well as those involved in DNA transposition and rearrangement, suggesting that this region may have been or is a mobile element. The transcriptional start sites of pagK, M, and J were determined; however, comparison to other known pag gene promoters failed to reveal a consensus sequence for PhoP-regulated activation. DNA sequences hybridizing to a Salmonella typhimurium pagK specific probe were found in S. enteritidis but absent in other Salmonella serotypes and Enterobacteriaceae tested, suggesting that these genes are specific for broad host range Salmonellae that cause diarrhoea in humans. Cumulatively, these data further demonstrate: (1) that PhoP-PhoQ is a global regulator of the production of diverse envelope or secreted proteins; (2) that PhoP-PhoQ regulate the production of proteins of redundant function; and (3) that pag are often located in regions of horizontally acquired DNA that are absent in other Enterobacteriaceae.

Characterization of plasmid regions of foodborne Yersinia enterocolitica biogroup 1A strains hybridizing to the Yersinia enterocolitica virulence plasmid

The aim of our study was to find out if plasmids of foodborne Yersinia enterocolitica biogroup 1A strains harbour genes related to the virulence genes located on the virulence plasmid pYV of Yersinia enterocolitica. The foodborne strains were isolated from pork, as pigs are considered as an important reservoir for enteropathogenic Y. enterocolitica 0:3 and 0:9 strains. The plasmids of the foodborne strains were characterized by restriction enzyme analysis and hybridized to the virulence plasmid pYV of pathogenic Y. enterocolitica strains (0:3 biogroup 4; 0:9 biogroup 2). In several cases the plasmids of the foodborne strains showed homologies to parts of the pYV plasmid. Analysis of the hybridizing regions revealed that genes involved in replication, sequences of transposable elements and an endonuclease gene caused the observed hybridization to the virulence plasmid. In cause of the study also a remnant of a Tn3-like transposon was shown to be present adjacent to the yadA gene on the pYV plasmid. Although there is evidence that at least some strains of Y. enterocolitica biogroup 1A might possess pathogenic properties none of the well known plasmid encoded virulence genes were present on the plasmids of the investigated foodborne biogroup 1A strains.

Yersinia enterocolitica-induced interleukin-8 secretion by human intestinal epithelial cells depends on cell differentiation

In response to bacterial entry epithelial cells up-regulate expression and secretion of various proinflammatory cytokines, including interleukin-8 (IL-8). We studied Yersinia enterocolitica O:8-induced IL-8 secretion by intestinal epithelial cells as a function of cell differentiation. For this purpose, human T84 intestinal epithelial cells were grown on permeable supports, which led to the formation of tight monolayers of polarized intestinal epithelial cells. To analyze IL-8 secretion as a function of cell differentiation, T84 monolayers were infected from the apical or basolateral side at different stages of differentiation. Both virulent (plasmid-carrying) and nonvirulent (plasmid-cured) Y. enterocolitica strains invaded nondifferentiated T84 cells from the apical side. Yersinia invasion into T84 cells was followed by secretion of IL-8. After polarized differentiation of T84 cells Y. enterocolitica was no longer able to invade from the apical side or to induce IL-8 secretion by T84 cells. However, Y. enterocolitica invaded and induced IL-8 secretion by polarized T84 cells after infection from the basolateral side. Basolateral invasion required the presence of the Yersinia invasion locus, inv, suggesting beta1 integrin-mediated cell invasion. After basolateral infection, Yersinia-induced IL-8 secretion was not strictly dependent on cell invasion. Thus, although the plasmid-carrying Y. enterocolitica strain did not significantly invade T84 cells, it induced significant IL-8 secretion. Taken together, these data show that Yersinia-triggered IL-8 secretion by intestinal epithelial cells depends on cell differentiation and might be induced by invasion as well as by basolateral adhesion, suggesting that invasion is not essential for triggering IL-8 production. Whether IL-8 secretion is involved in the pathogenesis of Yersinia-induced abscess formation in Peyer's patch tissue remains to be shown.

Emerging and reemerging infectious diseases: a multidisciplinary perspective

Predictions that infectious diseases would be eliminated as a major threat to human health have been shattered by emerging and reemerging infections, among them acquired immunodeficiency syndrome (AIDS), hemorrhagic fevers, marked increases in infections caused by antimicrobial-resistant bacteria, and the resurgence of tuberculosis and malaria. Understanding the dynamics of emerging and reemerging infections is critical to efforts to reduce the morbidity and mortality of such infections, to establish policy related to preparedness for infectious threats, and for decisions on where to use limited resources in the fight against infections. In order to offer a multidisciplinary perspective, 23 infectious disease specialists, epidemiologists, geneticists, microbiologists, and population biologists participated in an open forum at Emory University on emerging and reemerging infectious diseases. As summarized below, the group addressed questions about the definition, the identification, the factors responsible for, and multidisciplinary approaches to emerging and reemerging infections.

Contribution of the Mn-cofactored superoxide dismutase (SodA) to the virulence of Yersinia enterocolitica serotype O8

Enteric pathogens harbor a set of enzymes (e.g., superoxide dismutases [SOD]) for detoxification of endogenous and exogenous reactive oxygen species which are encountered during infection. To analyze the role of the Mn-cofactored SOD (SodA) in the pathogenicity of yersiniae, we cloned the sodA gene of Yersinia enterocolitica serotype O8 by complementation of an Escherichia coli sodA sodB mutant and subsequently constructed an isogenic mutant by allelic exchange. Sequence analysis revealed an open reading frame that enabled the deduction of a sequence of 207 amino acids with 85% identity to SodA of E. coli. In a mouse infection model, the sodA null mutant was strongly attenuated in comparison to its parental strain. After intravenous infection, the survival and multiplication of the mutant in the spleen and liver were markedly reduced. In contrast, inactivation of sodA had only minor effects on survival and multiplication in the gut and Peyer's patches, as could be demonstrated in the orogastric infection model. The reduction in virulence was accompanied by a low but significant increase of susceptibility of the soda mutant to bacterial killing by polymorphonuclear leukocytes (PMN) and an alteration of the intracellular chemiluminescence response of PMN. These results suggest that the resistance of Y. enterocolitica to exogenous oxygen radicals produced by phagocytes involves the Mn-cofactored SOD. The important role of sodA for the pathogenicity of Y. enterocolitica could also be due to detoxification of endogenous, metabolically produced oxygen radicals which are encountered by extracellular enteric pathogens during the invasion of the host.

A protective epitope of Moraxella catarrhalis is encoded by two different genes

The high-molecular-weight UspA protein of Moraxella catarrhalis has been described as being both present on the surface of all M. catarrhalis disease isolates examined to date and a target for a monoclonal antibody (MAb 17C7) which enhanced pulmonary clearance of this organism in a mouse model system (M. E. Helminen et al., J. Infect. Dis. 170:867-872, 1994). A recombinant bacteriophage that formed plaques which bound MAb 17C7 was shown to contain a M. catarrhalis gene, designated uspA1, that encoded a protein with a calculated molecular weight of 88,271. Characterization of an isogenic uspA1 mutant revealed that elimination of expression of UspA1 did not eliminate the reactivity of M. catarrhalis with MAb 17C7. In addition, N-terminal amino acid analysis of internal peptides derived from native UspA protein and Southern blot analysis of M. catarrhalis chromosomal DNA suggested the existence of a second UspA-like protein. A combination of epitope mapping and ligation-based PCR methods identified a second M. catarrhalis gene, designated uspA2, which also encoded the MAb 17C7-reactive epitope. The UspA2 protein had a calculated molecular weight of 62,483. Both the isogenic uspA1 mutant and an isogenic uspA2 mutant possessed the ability to express a very-high-molecular-weight antigen that bound MAb 17C7. Southern blot analysis indicated that disease isolates of M. catarrhalis likely possess both uspA1 and uspA2 genes. Both UspA1 and UspA2 most closely resembled adhesins produced by other bacterial pathogens.

Application of an enzyme immunoassay to monitor bacterial binding and to measure inhibition of binding to different types of solid surfaces

We describe the application of an enzyme immunoassay (EIA) for detecting bacteria bound to a solid surface. Different Yersinia enterocolitica and Escherichia coli strains, expressing the YadA protein, type 1 or type P fimbriae were used as models for this study. The assay was used to detect bacteria bound to fixed tissues or to glass slides coated with extracellular matrix molecules (collagen, laminin or fibronectin). E. coli specific antiserum (B357, Dakopatts, Glostrup, Denmark) and peroxidase conjugated antiserum (P217) were used to detect all E. coli strains used in the study. The bacterial binding could be monitored with a linear detection range between 10(5) and 10(8) bacteria. Most importantly, dose dependent inhibition of bacterial binding by soluble extracellular matrix molecules could be measured.

Virulence and arsenic resistance in Yersiniae

The genus Yersinia contains three pathogenic species: Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica. Only a few biotypes and serotypes of Y. enterocolitica are pathogenic, and these form two distinct groups: some are of low virulence, and they are encountered worldwide; others, mainly encountered in North America, are markedly more virulent. All pathogenic yersiniae possess a 70-kb virulence plasmid called pYV which encodes secreted antihost proteins called Yops as well as a type III secretion machinery that is required for Yop secretion. Genes encoding Yop synthesis and secretion are tightly clustered in three quadrants of the pYV plasmid. We show here that in the low-virulence strains of Y. enterocolitica, the fourth quadrant of the plasmid contains a new class II transposon, Tn2502. This transposon encodes a defective transposase, but transposition can be complemented in trans by Tn2501, another class II transposon. Tn2502 was not detected in the pYV plasmids of the more virulent American strains of Y. enterocolitica, of Y. pseudotuberculosis, and of Y. pestis. Tn2502 confers arsenite and arsenate resistance. This resistance involves four genes; three are homologous to the arsRBC genes present on the Escherichia coli chromosome, but no homolog of the fourth one, arsH, has been found. The systematic presence of such a resistance operon on a virulence plasmid is unusual and could be related to the recent spread of low-virulence Y. enterocolitica strains. The presence of this ars operon also constitutes the first significant difference between the pYV plasmids from different Yersinia species.

Passive immunity to infection with Yersinia spp. mediated by anti-recombinant V antigen is dependent on polymorphism of V antigen

The V antigen is a 37-kDa secreted polypeptide encoded on the 70-kb virulence plasmid of pathogenic Yersinia spp. Besides having regulatory functions, it is known to be a virulence factor and a protective antigen. DNA sequencing of the most common serotypes of human pathogenic Yersinia enterocolitica and Y. pseudotuberculosis revealed that two evolutionary distinct types of V antigen exist in Yersinia spp. One type is represented by Y. enterocolitica serotype 08 strains WA, WA-314, and NCTC 10938 (designated LcrV-YenO8); the other type comprises Y. pestis, Y. pseudotuberculosis, and Y. enterocolitica serotypes O3, O9, and O5,27 (LcrV-Yps). A hypervariable region between amino acids 225 and 232 represents the main difference between the two types. By raising monospecific antisera against both types of V antigen (anti-rVO8 and anti-rVO3), we were able to demonstrate that, in general, passive immunization of mice against a challenge with yersiniae was possible with both anti-Y. enterocolitica V antigen sera. However, anti-V antigen serum was protective only if the immunizing V antigen was the same type as the V antigen produced by the infective strain. The failure of the American V antigen type represented by Y. enterocolitica serotype O8 to protect against Yersinia spp. carrying the other V antigen type (LcrV-Yps) could be an explanation for the presence of plague foci in American countries.

Yersinia pestis--etiologic agent of plague

Plague is a widespread zoonotic disease that is caused by Yersinia pestis and has had devastating effects on the human population throughout history. Disappearance of the disease is unlikely due to the wide range of mammalian hosts and their attendant fleas. The flea/rodent life cycle of Y. pestis, a gram-negative obligate pathogen, exposes it to very different environmental conditions and has resulted in some novel traits facilitating transmission and infection. Studies characterizing virulence determinants of Y. pestis have identified novel mechanisms for overcoming host defenses. Regulatory systems controlling the expression of some of these virulence factors have proven quite complex. These areas of research have provide new insights into the host-parasite relationship. This review will update our present understanding of the history, etiology, epidemiology, clinical aspects, and public health issues of plague.

Reevaluation of the virulence phenotype of the inv yadA double mutants of Yersinia pseudotuberculosis

Yersinia pseudotuberculosis and Yersinia enterocolitica are closely related human pathogens causing gastroenteritis. Invasin and YadA are two of the most extensively studied virulence factors of the Yersinia genus. Invasin is the primary invasion factor encoded by the inv gene on the chromosome and is required for the penetration of the epithelial cells. YadA is encoded by the yadA gene on the 70-kb virulence plasmid and has multiple functions. Previous studies indicate that an inv yadA double mutant of Y. enterocolitica is avirulent while an inv yadA mutant of Y. pseudotuberculosis is hypervirulent. In this study, we investigated this unexpected difference. New constructs of the inv yadA mutants of Y. pseudotuberculosis were made and tested in mice. These new constructs were not hypervirulent; rather, they maintained the same virulence as the wild-type strain. Further examination of the inv mutant used for the previous study revealed that it carries an aberrant inv phenotype and has an altered outer membrane profile and an altered colony morphology. Therefore, the mutants used previously were not isogenic to the parental wild-type strain, which may in part account for the difference in the results obtained.