Characterization of common virulence plasmids in Yersinia species and their role in the expression of outer membrane proteins

Invasin expression in Yersinia pseudotuberculosis

A 3.2-kb region on the chromosome of Yersinia pseudotuberculosis, called inv, encodes invasin, a 103-kDa protein of the bacterial outer membrane. Invasin mediates bacterial entry into cultured animal cells. Six Y. pseudotuberculosis strains isolated from animal or human infections were analyzed for the presence of inv-related sequences with a radiolabeled inv clone, pRI203. We found that inv-specific sequences were present in all strains studied. Strains cured of virulence plasmid pYV were studied by Western immunoblot analysis with a monoclonal antibody directed against invasin. All but one strain produced invasin, but some strains produced more invasin than others. A strong correlation was found between the level of invasin production by these strains and their ability to enter into HEp-2 or CHO cells. The virulence of these strains was assessed in a murine model by measuring the number of bacteria in the spleen after intravenous challenge or in the mesenteric lymph nodes after intragastric challenge. The capacities of strains to invade cultured mammalian cells and to colonize the spleen were strongly correlative. In contrast, the ability of strains to translocate from the intestinal lumen to the mesenteric lymph nodes after intragastric inoculation did not correlate with their in vitro invasiveness.

Role of Yersinia enterocolitica Yst toxin in experimental infection of young rabbits

We constructed a Yst-negative mutant of Yersinia enterocolitica W1024 by reverse genetics, and we compared the virulence of the yst+ and yst isogenic strains in an experimental oral infection of the young rabbit. The rabbits infected with the yst+ strain suffered from the diarrhea and lost weight, and most of them died. By contrast, the occurrence of diarrhea, weight loss, and death in the group of rabbits infected with the yst mutant was as low as that in the group of uninfected rabbits. Bacteria from both strains were excreted in the feces and induced a serum antibody response against Yop proteins. The yst mutant disappeared more rapidly from the feces. We conclude that the enterotoxin Yst is a major factor involved in the Y. enterocolitica-associated diarrhea in the young rabbit. Given the similarity with the symptoms observed for children, this result suggests that Yst could also be an important factor in diarrhea in young children infected with Y. enterocolitica.

A novel protein, LcrQ, involved in the low-calcium response of Yersinia pseudotuberculosis shows extensive homology to YopH

The plasmid-encoded yop genes of pathogenic yersiniae are regulated by the environmental stimuli calcium and temperature. A novel protein, LcrQ, which exhibits a key function in the negative calcium-controlled pathway, was identified. DNA sequence analysis revealed that LcrQ has a molecular mass of 12,412 daltons and its isoelectric point is 6.51. Overexpression of LcrQ in trans in wild-type Yersinia pseudotuberculosis YPIII(pIB102) changed the phenotype from calcium dependence to calcium independence and inhibited Yop expression. LcrQ is expressed from a monocistronic operon. Trans overexpression of LcrQ in yopN and lcrH mutants affected the phenotype of the yopN mutant (temperature sensitive to calcium independence) but not that of the lcrH mutant (temperature sensitive), suggesting that LcrQ acts between YopN and LcrH in the calcium-regulated pathway. An lcrQ mutant was found to be temperature sensitive for growth and showed derepressed Yop expression at 37 degrees C in the presence of calcium in the growth medium. During these culture conditions, the lcrQ mutant secreted only LcrV and YopD into the culture supernatant. Removal of Ca2+ from the growth medium resulted in a Yop expression pattern of the mutant that was identical to that of the wild-type strain. The LcrQ protein was recovered from the culture supernatant. LcrQ shows 42% identity to the first 128 amino acids of the YopH virulence protein.

Bacterial resistance to complement killing mediated by the Ail protein of Yersinia enterocolitica

Ail is a 17-kDa outer membrane Yersinia protein that mediates bacterial attachment to, and invasion of, cultured epithelial cells. We report here an alternative role for Ail in the pathogenesis of Yersinia infection. We found that Escherichia coli HB101 harboring the 4-kilobase recombinant ail clone pVM102 were highly resistant to killing in up to 50% normal human serum. A 674-base-pair fragment of DNA from pVM102, which encodes the ail gene, was inserted into pUC18 and shown to promote full resistance to complement killing in E. coli HB101. Cellular attachment and resistance to complement killing in a plasmid-cured inv- strain of Yersinia enterocolitica (0:8) was correlated with the thermoinduced expression of Ail at 37 degrees C. Insertional inactivation of ail in Y. enterocolitica resulted in loss of both thermoinduced bacterial properties. Cellular attachment and serum resistance were restored by complementation of the defect by plasmid-encoded ail. Complementation of cell attachment activity required bacterial growth at 37 degrees C, indicating that an additional thermoinduced factor is required for this Ail function. In addition, these studies reveal that functional homology exists between Ail and the structurally related protein Rck, which promotes resistance to complement killing in Salmonella typhimurium.

The difference in the lcrV sequences between Y. pestis and Y. pseudotuberculosis and its application for characterization of Y. pseudotuberculosis strains

We have sequenced the lcrGVH operon from Y. pseudotuberculosis plasmid pYV995 and compared its sequence with that of Y. pestis. The sequences were highly homological, however, six base pair substitutions were found in one short 14 bp region termed variable sequence. Two oligonucleotides corresponding to variable sequence of Y. pestis (pes-V) or Y. pseudotuberculosis (ptb-V) were synthesized and were used as molecular probes in hybridization experiments with sets of Y. pestis and Y. pseudotuberculosis strains. All 17 Y. pestis strains tested were positive only with the pes-V probe, 18 of 21 Y. pseudotuberculosis strains were positive with the ptb-V probe, while three Y. pseudotuberculosis strains reacted with the pes-V probe but not the ptb-V probe. The 200 bp fragment including variable sequence was sequenced in seven Y. pseudotuberculosis strains. The Y. pseudotuberculosis strains which were positive with the pes-V probe possessed the 200 bp fragment sequence almost identical with that from Y. pestis. No correlation between the Y. pestis-like lcrV sequence and virulence was found for these strains. Moreover, the Y. pseudotuberculosis strains with Y. pestis-like sequences in contrast to Y. pestis possessed unaltered yadA gene. However, we have found the yadA frameshift mutation characteristic for Y. pestis in one Y. pseudotuberculosis strain 312.

Binding of cultured mammalian cells to immobilized bacteria

The invasin protein of Yersinia pseudotuberculosis binds to integrin receptors on mammalian cells and promotes cellular penetration. We demonstrate here that the cell attachment activity of invasin can be detected in bacterial colonies that have been immobilized on filter membranes. Invasin expressed in either Escherichia coli K-12 or Y. pseudotuberculosis mediated binding to membranes, and as few as 10(5) Y. pseudotuberculosis resulted in detectable attachment of cultured epithelial cells. A similar binding activity was detected in clinical isolates of the related pathogen Y. enterocolitica but not in environmental isolates. Although there exist multiple mechanisms for the binding of wild-type organisms to host cells, efficient mammalian cell binding to immobilized Y. pseudotuberculosis required expression of a functional invasin protein. Several pathogens that are known to bind or penetrate mammalian cells were also tested, and only one of these bound cultured mammalian cells efficiently.

The Salmonella typhimurium virulence plasmid complement resistance gene rck is homologous to a family of virulence-related outer membrane protein genes, including pagC and ail

A fragment of the Salmonella typhimurium virulence plasmid containing the rck locus, when cloned in the recombinant cosmid pADE016, was shown previously to confer high-level complement resistance on both rough and smooth Escherichia coli, Salmonella minnesota, and S. typhimurium and was associated with the production of an outer membrane protein. We determined the nucleotide sequence of the fragment containing the rck locus. Mutations in the two major open reading frames confirmed that the complement resistance mediated by pADE016 was due to a single 555-bp rck gene encoding a 17-kDa outer membrane protein. Analysis of the rck gene revealed that the Rck outer membrane protein consisted of 185 amino acid residues, with a calculated postcleavage molecular mass of 17.4 kDa. Rck is homologous to a family of outer membrane proteins expressed in gram-negative bacteria, two of which have been associated with virulence-related phenotypes: PagC, required by S. typhimurium for survival in macrophages and for virulence in mice; and Ail, a product of the Yersinia enterocolitica chromosome capable of mediating bacterial adherence to and invasion of epithelial cell lines. Rck, most closely related to PagC, represents the third outer membrane protein in this five-member family with a distinct virulence-associated phenotype.

Surface-exposed antigenic determinants in outer membranes of wild Yersinia pestis isolates

Immunogenic surface exposed envelope proteins of Yersinia pestis strains were investigated with SDS-PAGE and immunoblots with antisera of immunized guinea pigs and convalescent patients. The sarkosyl-insoluble outer membrane proteins (OMPs) of three human isolates and one laboratory strain of Y. pestis grown in different rich media to exponential or stationary phase, and cultivated at 28 degrees C or 37 degrees C, were assayed for the presence of immunogenic peptides. Seven guinea-pig sera immunized with one of the four Y. pestis strains and four human sera from plague-infected patients indicated that at least four outer membrane proteins with molecular weights of 45 KDal, 42 KDal, 21 KDal and 16.5 KDal were strongly recognized by at least one of them. All but one of the guinea-pig serum and one human serum recognized the 45 KDal protein. The 42 KDal was identified only in outer membrane isolated from Y. pestis cells grown at 28 degrees C. All immunogenic OMPs were found in the four strains investigated. Labelling of intact Y. pestis cells with Iodogen and 131I further demonstrated the surface-exposed location of the immunogenic OMPs.

Intracellular targeting of the Yersinia YopE cytotoxin in mammalian cells induces actin microfilament disruption

Pathogenic Yersinia spp., including the etiological agent of plague, Y. pestis, all carry a common plasmid that encodes a number of essential virulence determinants, the Yop proteins. One of these, YopE, has been shown to be involved in the obstruction of the primary host defense by a molecular mechanism leading to inhibition of phagocytosis (R. Rosqvist, A. Forsberg, M. Rimpiläinen, T. Bergman, and H. Wolf-Watz, Mol. Microbiol. 4:657-667, 1990). Although the Yop proteins are secreted into the culture supernatant in vast amounts, in vitro studies of the function of the Yop proteins have so far been unsuccessful. We show that isolated Yop proteins indeed can cause cytotoxic effects in vitro if the proteins are introduced intracellularly into the eukaryotic cell. Isolated Yop proteins of Yersinia pseudotuberculosis were found to disrupt the microfilament structure when microinjected intracellularly into the host cell. In particular, YopE was demonstrated to be directly involved in the cytotoxic action, whereas YopD seems to have a critical role in translocating the YopE protein through the host cell membrane. These results elucidate the requirement for at least some of the Yop proteins to leave the pathogen during infection.

LcrD, a membrane-bound regulator of the Yersinia pestis low-calcium response

Yersinia pestis, the etiologic agent of bubonic plague, contains a 75-kb virulence plasmid, called pCD1 in Y. pestis KIM. The low-Ca(2+)-response genes of Y. pestis regulate both bacterial growth and the expression of pCD1-encoded virulence determinants in response to temperature and the presence of Ca2+ or nucleotides. This study characterizes the nucleotide sequence and protein product of the lcrD locus. An lcrD mutant, in contrast to the parent Y. pestis, did not undergo growth restriction or induce strong expression of the V antigen when grown under conditions (37 degrees C, no Ca2+) expected to elicit maximal expression of pCD1 genes. DNA sequence analysis of the cloned lcrD locus showed a single open reading frame that could encode a protein with a molecular weight of 77,804 and a pI of 4.88. LcrD was identified as a 70-kDa inner membrane protein by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis. LcrD membrane topology was investigated by using lcrD-phoA translational fusions generated with the transposon TnphoA. The alkaline phosphatase activities of the resultant hybrid proteins were consistent with a model predicting eight amino-terminal transmembrane segments that anchor a large cytoplasmic carboxyl-terminal domain to the inner membrane.

Recognition by peptide mapping of three different structural groups of outer membrane protein YOP-1 of Yersinia enterocolitica and Yersinia pseudotuberculosis

The structural relation of YOP-1 of "european" and "american" Yersinia enterocolitica serotypes O:3, O:9, O:5,27, and O:8 and O:20, respectively, and Y. pseudotuberculosis serotypes I, II, and III was compared by sodium dodecyl sulfate polyacrylamide gel electrophoresis and peptide mapping using Staphylococcus aureus protease V8. Apparent molecular weights of YOP-1 ranged from 206,000 (O:3) to approx. 180,000 (O:8). According to their respective peptide maps YOP-1 of the "european" and "american" Y. enterocolitica serotypes and Y. pseudotuberculosis serotypes could be assigned to three different groups. Evaluation of several isolates of Y. enterocolitica serotypes O:3, O:9, and O:8 by peptide mapping indicated that YOP-1 is conserved within a serotype. However, one serotype O:8 isolate differed from the consensus peptide pattern of the other serotype O:8 and O:20 isolates. The similarity of the peptide patterns of Yersinia serotypes which predominate in certain geographical locations, i.e., "european" and "american" Y. enterocolitica serotypes, suggest common evolution of YOP-1 of these serotypes independent of the evolution of the other serotypes.

Factors promoting acute and chronic diseases caused by yersiniae

The experimental system constructed with the medically significant yersiniae provides a powerful basic model for comparative study of factors required for expression of acute versus chronic disease. The system exploits the close genetic similarity between Yersinia pestis, the etiological agent of bubonic plague, and enteropathogenic Yersinia pseudotuberculosis and Yersinia enterocolitica. Y. pestis possesses three plasmids, of which one, shared by the enteropathogenic species, mediates a number of virulence factors that directly or indirectly promote survival within macrophages and immunosuppression. The two remaining plasmids are unique and encode functions that promote acute disease by enhancing bacterial dissemination in tissues and resistance to phagocytosis by neutrophils and monocytes. These properties are replaced in the enteropathogenic yersiniae by host cell invasins and an adhesin which promote chronic disease; the latter are cryptic in Y. pestis. Additional distinctions include specific mutational losses in Y. pestis which result in loss of fitness in natural environments plus gain of properties that facilitate transmission and infection via fleabite.

Class-specific immune response to Yersinia enterocolitica serotype O9 antigens as determined by enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) using lipopolysaccharide (S-LPS) as the antigen was used to analyze the antibody response in rabbits orogastrically and intravenously infected with virulent (plasmid-bearing) Yersinia enterocolitica O9 strains (pYV+) and with the avirulent (plasmid-cured) derivatives (pYV-). A significative response of immunoglobulin G (IgG), IgA, and IgM antibodies against the S-LPS antigen was evident in sera from the rabbits orogastrically infected with pYV+ strains. This immune response was stronger and persisted longer than those obtained with the corresponding pYV- strains. In contrast, few differences were observed in the titers and evolution of IgG, IgA, and IgM antibodies against the S-LPS antigen in rabbits intravenously infected with pYV+ and pYV- strains. These results suggest that the necessity of the virulence plasmid for the establishment of infection by Y. enterocolitica serotype O9 is conditioned by the infection route used. When the S-LPS ELISA was compared with the radial immunodiffusion test using the native hapten as the antigen, the results showed that the ELISA technique was more sensitive. However, only those sera obtained between 2 and 8 weeks postinfection from rabbits intravenously infected with plasmid-bearing strains were positive in the radial immunodiffusion test.

ymoA, a Yersinia enterocolitica chromosomal gene modulating the expression of virulence functions

The virulence functions of Yersinia enterocolitica include the pYV-encoded Yop proteins and YadA adhesin as well as the chromosome-encoded enterotoxin, Yst. The yop and yadA genes form a temperature-activated regulon controlled by the transcriptional activator VirF. Gene virF, also localized on pYV, is itself thermoinduced in the absence of other pYV genes. The enterotoxin yst gene is silent in some collection strains including strain W22703. This paper describes two Tn5-Tc1 chromosomal insertion mutants of W22703 transcribing virF, and hence the yop and yadA genes, at low temperature. These mutants also resumed their production of Yst, with its typical temperature dependence. Both mutations were insertions in the same gene called ymoA for 'Yersinia modulator'. The cloned ymoA gene fully complemented the two mutations. Several properties of the mutants suggest that ymoA encodes a histone-like protein. According to the nucleic acid sequence, the product of ymoA is an 8064 Da protein rich in aspartic acid (9%), glutamic acid (9%) and lysine (10.5%), but the predicted amino acid sequence shows no similarity with any described histone-like protein. This work supports recent reports which propose a role for DNA topology and bacterial chromatin structure in thermoregulation of virulence functions.

Relationship between clinical and milk isolates of Yersinia enterocolitica

In the summer of 1987-1988, an outbreak of 11 cases of Yersinia enterocolitica enteritis caused by 2 serogroups (0:3, 0:6,30) occurred prompting an investigation into possible environmental sources. Symptoms were present for a mean of 9 days and occurred in 2 distinct age groups--toddlers (7) who presented with diarrhea, and young adults (4), 3 of whom presented clinically with appendicitis. In a survey of 39 randomly chosen pasteurized milk samples, 9 were positive for growth of Y. enterocolitica and 1 each for Y. fredericksenii and Y. intermedia. An association between clinical and milk isolates of Y. enterocolitica was thus sought by comparison of biogroups, serogroups, virulence markers and biochemical and outer membrane profiles. All milk isolates belonged to biogroup 1, serogroup 0:6,30. Pathogenicity studies on the 0:6,30 serogroup isolates from feces and milk were performed with 3 in-vitro tests (Ca2+ dependency, autoagglutination, & serum resistance). The human isolates were positive in most of the 3 tests whilst none of the milk isolates were positive. Outer membrane protein analysis of 0:6,30 from human and milk isolates showed similar profiles suggesting a possible association, however the environmental source of the majority of isolates (0:3) remains unknown.

The Yersinia pestis V antigen is a regulatory protein necessary for Ca2(+)-dependent growth and maximal expression of low-Ca2+ response virulence genes

The low-Ca2+ response is a multicomponent virulence regulon of the human-pathogenic yersiniae in which 12 known virulence genes are coordinately regulated in response to environmental cues of temperature, Ca2+, and nucleotides such as ATP. Yersinial growth also is regulated, with full growth yield being permitted at 37 degrees C only if Ca2+ or a nucleotide is present. In this study, we constructed and characterized a mutant Yersinia pestis specifically defective in the gene encoding the V antigen, one of the virulence genes of the low-Ca2+ response. An in-frame internal deletion-insertion mutation was made by removing bases 51 through 645 of lcrV and inserting 61 new bases. The altered lcrV was introduced into the low-Ca2+ response plasmid in Y. pestis by allelic exchange, and the resulting mutant was characterized for its two-dimensional protein profiles, growth, expression of an operon fusion to another low-Ca2+ response virulence operon, and virulence in mice. The mutant had lost its Ca2+ and nucleotide requirement for growth, showed diminished expression of Ca2(+)-and nucleotide-regulated virulence genes, and was avirulent in mice. The mutation could be complemented with respect to the growth property by supplying native V antigen operon sequences in trans in high copy number (on pBR322). Partial complementation of the growth defect and almost complete complementation of the virulence defect were seen with a lower-copy-number complementing replicon (a pACYC184 derivative). The data are consistent with the interpretation that V antigen is bifunctional, with a role in regulating growth and expression of low-Ca2+ response virulence genes in addition to its putative role as a secreted virulence protein.

Analysis of the V antigen lcrGVH-yopBD operon of Yersinia pseudotuberculosis: evidence for a regulatory role of LcrH and LcrV

Virulent Yersinia species possess a common plasmid that encodes essential virulence determinants (Yops) which are regulated by the extracellular stimuli Ca2+ and temperature. The V antigen operon was recently shown to be involved in the Ca2(+)-regulated negative pathway (A. Forsberg and H. Wolf-Watz, Mol. Microbiol. 2:121-133, 1988). We show here that the V antigen-containing operon of Yersinia pseudotuberculosis is a polycistronic operon having the gene order lcrGVH-yopBD. DNA sequencing analysis of lcrGVH revealed a high homology to the corresponding genes of Yersinia pestis. LcrG was conserved and LcrH showed only one amino acid difference, while LcrV showed only 96.6% identity. The amino acid substitutions of LcrV occurred in the central domain of the protein, while the two ends of the protein were conserved. Northern (RNA) blotting experiments showed that the operon is regulated at the transcriptional level by the extracellular stimuli temperature and calcium. One 4.6-kb transcriptional product of the operon was identified. This mRNA is rapidly processed at its 5' end, resulting in different mRNA species of variable stability. By genetic analysis, the lcrV and lcrH gene products were found to be regulatory proteins having important roles in the Ca2(+)-controlled regulation of Yop expression. The activity of LcrH is modulated by a gene product of the operon that inhibits the negative action of LcrH on yop transcription in the absence of Ca2+.

Tyrosine phosphate hydrolysis of host proteins by an essential Yersinia virulence determinant

The plasmid-encoded YopH protein is a protein-tyrosine phosphatase (PTPase; EC 3.1.3.48) that is essential for Yersinia virulence. We have investigated the molecular basis for the role of PTPase activity in Yersinia pathogenesis. Allelic recombination was employed to introduce a defined mutation into the yopH plasmid gene. Conversion of the essential Cys-403 to Ala in the catalytic domain of the protein abolished YopH PTPase activity and significantly reduced the virulence of Yersinia pseudotuberculosis in a murine infection model. 32P-labeled phosphotyrosine-containing proteins were immunoprecipitated from extracts of Y. pseudotuberculosis-infected cell monolayers and analyzed by SDS/PAGE to assess the impact of YopH on host protein phosphorylation. Major proteins of 200, 120, and 60 kDa were dephosphorylated in macrophages associated with wild-type Y. pseudotuberculosis. Selective removal of phosphate from the 120- and 60-kDa proteins was shown to be specific to the YopH PTPase activity. Phagocytosis of the bacteria was not required for this dephosphorylation activity, suggesting that YopH is functionally expressed by extracellular bacteria. These observations indicate that the essential function of YopH in Yersinia pathogenesis is host-protein dephosphorylation.

Calcium-responsive expression of plasmid-mediated outer membrane proteins from Yersinia enterocolitica grown on solid media

In vitro synthesis of proteins directed by Yersinia enterocolitica virulence plasmid DNA was studied using a cell-free Escherichia coli coupled transcription-translation system. Out of a total of twenty-four polypeptides synthesized in vitro, ten were identified (based on virtually identical molecular masses) as outer membrane proteins synthesized in vivo when virulent plasmid-bearing Y. enterocolitica cells were grown on four different solid media. Two high molecular weight outer membrane proteins synthesized in vivo by plasmid-bearing cells were not detected in the in vitro protein synthesizing system. Different plasmid-mediated outer membrane proteins were expressed in vivo in Y. enterocolitica grown on different media. Y. enterocolitica grown on media with high calcium concentration (1.4-1.5 mM) expressed twice the number of lower molecular weight outer membrane proteins than the organism grown on low calcium (238-311 microM) media. This is the first report that a single serotype has been shown to synthesize all the reported virulence plasmid-encoded outer membrane proteins including three new polypeptides. The constituents in the medium as well as the level of calcium appeared to have a regulatory role in plasmid gene expression for lower molecular weight outer membrane proteins.

Autoantibodies to the HLA-B27 sequence cross-react with the hypothetical peptide from the arthritis-associated Shigella plasmid

We previously reported elevated serum antibody levels to a peptide representing the HLA-B27 polymorphic region (B27 peptide) in HLA-B27(+) ankylosing spondylitis (AS) patients. A plasmid (pHS-2) isolated from arthritogenic Shigella flexneri strains had been shown to encode an amino acid sequence homologous to HLA-B27. Rabbit antibody to this sequence (pHS-2 peptide) strongly cross-reacted with B27 peptide and, to a much lesser extent, with Klebsiella nitrogenase peptide. Serum antibody levels to pHS-2 peptide were studied in 160 spondylarthropathy patients. 12 of 115 (10.4%) AS patients, 2 of 45 (4.4%) patients with Reiter's syndrome or reactive arthritis as well as 6 of 147 (4.1%) normal controls were shown to have elevated anti-pHS-2 peptide antibodies. Antibody levels to B27 and pHS-2 peptides were significantly correlated in 134 HLA-B27(+) patients (r = 0.333, P less than 0.001). 13 of 15 affinity-purified anti-B27 peptide antibodies from patients strongly cross-reacted with pHS-2 peptide, whereas only 3 weakly cross-reacted to nitrogenase peptide. Leucine appeared to be a critical residue for this cross-reaction. AS patients' anti-B27 peptide antibodies reacted with HLA-B27 transfected L cells. These results may suggest that pHS-2 peptide more efficiently "mimics" B27 peptide than does nitrogenase peptide. Involvement of pHS-2 in pathogenesis of spondylarthropathy through molecular mimicry mechanisms requires further study.

Protein tyrosine phosphatase activity of an essential virulence determinant in Yersinia

Yersinia is the genus of bacteria that is the causative agent in plague or the black death, and on several occasions this organism has killed a significant portion of the world's population. An essential virulence determinant of Yersinia was shown to be a protein tyrosine phosphatase. The recombinant 50-kilodalton Yersinia phosphatase had a specificity for removal of phosphate from Tyr-containing as opposed to Ser/Thr-containing phosphopeptides and proteins. Site-directed mutagenesis was used to show that the Yersinia phosphatase possesses an essential Cys residue required for catalysis. Amino acids surrounding an essential Cys residue are highly conserved, as are other amino acids in the Yersinia and mammalian protein tyrosine phosphatases, suggesting that they use a common catalytic mechanism.

Identification of a conjunctivitis-associated gene locus from the virulence plasmid of Yersinia enterocolitica

The virulence plasmid (pYV) of Yersinia enterocolitica is necessary for production of conjunctivitis in guinea pigs and for mouse lethality. To identify the genes responsible for production of conjunctivitis in guinea pigs, we subcloned the BamHI and SalI restriction fragments of the virulence plasmid of Y. enterocolitica A2635 (serotype O:8) into derivatives of the broad-host-range plasmid pRK290 and introduced the constructions into plasmid-negative Y. enterocolitica strains. A mild, transient conjunctivitis was evident 24 h after inoculation with strains containing a 2.8-kilobase (kb) BamHI fragment of pYV. These strains were cytotoxic to HEp-2 cells but did not cause death in iron-loaded adult mice. When the 2.8- and adjacent 0.5-kb BamHI fragments were deleted from the virulence plasmid of a fully virulent Y. enterocolitica isolate, the resultant strain did not cause conjunctivitis in guinea pigs and was not cytotoxic to HEp-2 cells. However, the strain with the deletion appeared to be more virulent for mice, with more rapid dissemination after orogastric inoculation, compared with that of the parent strain. When the deletion was complemented by introduction of a plasmid containing the 2.8-kb BamHI fragment, the strain again caused conjunctivitis but had decreased virulence for mice.

lcrR, a low-Ca2(+)-response locus with dual Ca2(+)-dependent functions in Yersinia pestis

The low-Ca2+ response (Lcr) of Yersinia includes a regulatory cascade and a set of virulence-related proteins, one of which is the V antigen. The regulatory genes modulate both bacterial growth and expression of the virulence-related proteins in response to temperature and the presence of Ca2+ and nucleotides. In this study we defined a new Lcr locus, lcrR, in Yersinia pestis KIM. An lcrR mutant, obtained by insertion mutagenesis, failed to grow at 37 degrees C whether Ca2+ was present or not. However, it grew normally in the presence of ATP, showing that the Ca2(+)- and nucleotide-responsive mechanisms are separate in Y. pestis. The lcrR mutant was avirulent in mice, probably due to its compromised growth at 37 degrees C. beta-Galactosidase measurements and Northern (RNA blot) analysis revealed that lcrR transcription was regulated primarily by temperature. The DNA sequence of the lcrR locus contained a single open reading frame of 441 bases that could encode a protein with a molecular weight of 16,470 and a pI of 10.73. Expression of an lcrR-containing clone in Escherichia coli yielded a 16,000-molecular-weight protein. At 37 degrees C, the lcrR mutant strongly expressed V antigen and initiated lcrGVH transcription whether Ca2+ was present or not, indicating that this mutant had lost the transcriptional downregulation of lcrGVH shown by the parent in the presence of Ca2+. In the absence of Ca2+, the mutant failed to express LcrG, even though lcrGVH mRNA initiated upstream of lcrG at the normal sites. These data suggest that the lcrR locus is necessary for the regulation of LcrG expression in the absence of Ca2+. Therefore, this locus has a dual regulatory role in the low-Ca2+ response.

Genetic evidence that the yopA gene-encoded Yersinia outer membrane protein Yop1 mediates inhibition of the anti-invasive effect of interferon

HEp-2 cell monolayers were challenged with genetic variants of Yersinia pseudotuberculosis YPIII(pIB1) and Yersinia enterocolitica W22708(pYL4). Both strains were represented by (i) variants harboring the 70-kilobase virulence plasmid, (ii) their isogenic plasmid-cured derivatives, and (iii) two transposon mutants constructed by insertional inactivation of the plasmid genes encoding outer membrane protein Yop1 and Ca2+ dependency in strains YPIII(pIB1) and W22708(pYL4). When the HEp-2 cells were pretreated with recombinant alpha interferon subtype A, all invasive variants of Y. enterocolitica and Y. pseudotuberculosis, except those variants which expressed Yop1, showed a significantly reduced ability to localize intracellularly. The anti-invasive effect of interferon was abolished when the gene was expressed or when a sterile filtered sonic extract of a Yop1-producing strain was added to the cell cultures. To obtain further evidence of a potential role of Yop1, a DNA fragment encoding Yop1 cloned into the vector pBR322 was used. After introduction of the resultant recombinant plasmid pYMS2 into the plasmid-cured variant YPIII and the Yop1-negative transposon mutant YPIII(pIB102) of Y. pseudotuberculosis, both transformants regained the ability to produce Yop1 and showed complete inhibition of the interferon effect. Moreover, the sterile sonic extract of an Escherichia coli strain, which carried pYMS2, neutralized the anti-invasive effect of interferon. The results provide direct genetic evidence that Yop1 mediates inhibition of the anti-invasive effect of interferon in HEp-2 cell cultures. The results also demonstrated that Yop1 itself reduces the ability of Yersinia spp. to localize intracellularly in HEp-2 cells.

Differentiation of serological responses to Yersinia enterocolitica serotype O9 and Brucella species by immunoblot or enzyme-linked immunosorbent assay using whole bacteria and Yersinia outer membrane proteins

Serum samples from 134 patients showing by the microagglutination test serological cross-reactivity between Yersinia enterocolitica serotype O9 and Brucella spp. were analyzed by immunoblot and enzyme-linked immunosorbent assay techniques for the presence of antibodies directed against plasmid-encoded, yersinia-associated outer membrane proteins (OMPs). Since these OMPs are exclusively expressed in pathogenic strains of Yersinia spp., this characteristic was chosen for serological differentiation of infections caused by these bacteria. The presence of antibodies against plasmid-encoded OMPs of pathogenic Yersinia spp. in patient sera appeared to be a suitable means to identify acute or recent infection with Y. enterocolitica serotype O9, whereas the failure to detect such antibodies indicated an acute or recent infection with Brucella spp.

Structural and functional similarities between the replication region of the Yersinia virulence plasmid and the RepFIIA replicons

We sequenced the minimum replication region of the virulence plasmid pYVe439-80 from a serogroup O:9 Yersinia enterocolitica. This sequence is 68% homologous on a 1,873-nucleotide stretch to the sequence of the RepFIIA replicon of the resistance plasmid R100. The sequence contains two open reading frames, repA and repB, encoding proteins of 33,478 and 9,568 daltons, respectively. The amino acid sequences of the two proteins are 77 and 55% identical, respectively, to proteins RepA1 and RepA2 of the R100 replicon. Analysis of minicells transformed with a copy number mutant demonstrated that the replication region of pYVe439-80 directs the synthesis of a 33-kilodalton protein. Disruption of repA, encoding this protein, abolished replication. Two regions of pYVe439-80 are 76 and 70% homologous, respectively, to the copy number control antisense RNA and to the origin of replication region of R100. A mutation introduced in the pYVe439-80 DNA corresponding to the R100 sequence encoding the copy number control antisense RNA resulted in an increase in copy number, indicating a functional homology between the two replicons.

Demonstration of cross-reactivity between bacterial antigens and class I human leukocyte antigens by using monoclonal antibodies to Shigella flexneri

Bacterial envelope proteins which share immunodeterminants with the human leukocyte antigen (HLA) class I histocompatibility antigen HLA-B27 may invoke spondyloarthritic disease through the process of molecular mimicry in patients expressing this phenotype. Monoclonal antibodies generated by the immunization of BALB/c mice with envelope proteins of Shigella flexneri type 2a were tested for reactivity against cultured lymphoblastoid cell lines of defined HLA phenotype. As measured by flow microfluorometry, four immunoglobulin M monoclonal antibodies reacted preferentially with HLA-B27-positive lymphocytes (HOM-2, MM) as compared with a B27-loss mutant line (1065) or cells lacking major histocompatibility complex class I antigen (Daudi, K562). Monoclonal antibodies also reacted with mouse EL-4 cells transfected with and expressing the HLA-B7 gene. Western immunoblot analysis of isolated enterobacterial envelopes demonstrated that the reactive epitope was present on bacterial proteins with an apparent relative molecular mass of 36 and 19 kilodaltons. The structural basis for the cross-reactivity of bacterial antigen and HLA-B27 appeared to reside in the portion of the HLA molecule that is responsible for allotypic specificity (amino acids 63 through 83), since monoclonal antibodies were positive by enzyme-linked immunosorbent assay with synthetic polypeptides corresponding to this segment.

Homologous DNA sequences on the virulence plasmids of pathogenic Yersinia and Salmonella dublin lane

Yersinia and Salmonella harbour plasmids that encode traits important for virulence, enabling both pathogenic genera to survive and grow in cells of the reticulo-endothelial organs during systemic infections. We have detected DNA homology between the Salmonella dublin virulence plasmid pSDL2 and the plasmids of the pathogenic Yersinia species pestis, pseudotuberculosis, and enterocolitica. Three regions of pSDL2 were found to share homology with the virulence plasmid pIB1 of Yersinia pseudotuberculosis. Two separate hybridizing segments mapped within the previously characterized 6.4 kb vir region of pSDL2 in the SalI B fragment. The third homologous region involved the replicon of pIB1, which hybridized to the SalI C2 fragment of pSDL2. The virulence plasmid pCD1 from Y. pestis showed similar homology with the three regions of pSDL2. Homologies to the vir and SalI C2 regions of pSDL2 were also found on plasmids from Yersinia enterocolitica serotypes 0:9, 0:3 and 0:5, 27. The discovery of separate homologous regions on the virulence plasmids of Salmonella and Yersinia suggests a distant evolutionary relationship.

The cytotoxic protein YopE of Yersinia obstructs the primary host defence

It has previously been shown that the plasmid-encoded YopE protein of Yersinia pseudotuberculosis is a virulence determinant. In this study, HeLa cells, macrophages and mice were used as different model systems to determine the actual role of YopE in the virulence process. The YopE protein mediates a cytotoxic response on a confluent layer of HeLa cells. A prerequisite of this activity is that the pathogen binds to the cell surface. YopE also induces a cytotoxic response on mouse macrophages where it influences the ability of the pathogen to resist phagocytosis. Bacterial mutants defective in their ability to express YopE are avirulent after oral or intraperitoneal infection but virulent following intravenous injection. On the basis of these results, we propose a role for YopE in the virulence process of Yersinia.

Identification of an Escherichia coli genetic locus involved in thermoregulation of the pap operon

We previously showed, using a single-copy papBAp-lac fusion (previously designated papBA-lac), that pyelonephritis-associated pili (pap) pilin gene transcription is subject to both phase variation and thermoregulatory control mechanisms (L. B. Blyn, B. A. Braaten, C. A. White-Ziegler, D. H. Rolfson, and D. A. Low, EMBO J. 8:613-620, 1989). At 37 degrees C, Escherichia coli strains carrying the papBAp-lac fusion displayed both Lac+ and Lac- colony phenotypes. In contrast, at 23 degrees C, colonies displayed a uniform Lac- phenotype, suggesting that pilin was not transcribed at this temperature. In this study, a strain carrying the papBAp-lac fusion was subjected to mini-Tn10 (mTn10) mutagenesis to isolate mutants that could initiate transcription of pilin at the nonpermissive temperature. Two classes of thermoregulatory mutants were identified in which the mTn10 mutation was linked to the mutant phenotype. Class I mutants displayed a phase variation phenotype at both 37 degrees C and 23 degrees C, whereas class II mutants displayed a uniform Lac+ colony phenotype at both temperatures. Preliminary analysis of these mutants showed that the mTn10 insertions in the class I mutants were chromosomally located, whereas the mTn10 insertions in the class II mutants were located within the papBAp-lac fusion phage. Southern blot analysis of the class I mutants demonstrated that mTn10 was present in the same 5.9-kilobase SalI DNA fragment in each mutant. Two of the class I mTn10 mutations were mapped to approximately 23.4 min on the E. coli K-12 chromosome. The locus defined by the class I mTn10 mutations was designated tcp, for thermoregulatory control of pap. Analysis of phase transition rates of the class I mutants showed that the phase-off (Lac-)----phase-on (Lac+) transition rates were higher than those observed with the nonmutant E. coli strain.

Comparative studies of Yersinia pestis outer membrane isolation techniques and their potential use in plaque epidemiology

In the present study three techniques for obtaining outer membrane enriched fractions from Yersinia pestis were evaluated. The techniques analysed were: differential solubilization of the cytoplasmic membrane with Sarkosyl or Triton X-100, and centrifugation in sucrose density gradients. The sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of outer membrane isolated by the different methods resulted in similar protein patterns. The measurement of NADH-dehydrogenase and succinate dehydrogenase (inner membrane enzymes) indicated that the outer membrane preparations obtained by the three methods were pure enough for analytical studies. In addition, preliminary evidences on the potential use of outer membrane proteins for the identification of geographic variants of Y. pestis wild isolates are presented.

Genetic analysis of the yopE region of Yersinia spp.: identification of a novel conserved locus, yerA, regulating yopE expression

The yopE gene of Yersinia pseudotuberculosis was recently sequenced, and YopE was identified as an indispensable virulence determinant when tested in a mouse model (A. Forsberg and H. Wolf-Watz, Mol. Microbiol. 2:121-133, 1988). In the study described here, the DNA sequences of the yopE genes of Yersinia pestis EV76 and Yersinia enterocolitica 8081 were determined and compared with that of the Y. pseudotuberculosis gene. Only two codons were found to differ, both leading to amino acid replacements, when the gene from Y. pestis was compared. These two replacements were also present in the gene from Y. enterocolitica; in addition, 18 other codons were found to differ. Thirteen of these substitutions led to amino acid replacements. Downstream of the yopE gene, the plasmid partition locus par was found to be conserved in all three species. In Y. enterocolitica 8081, the sequence homology was interrupted by a putative insertion sequence element inserted between the yopE gene and the par region at a position only 5 base pairs downstream of the yopE stop codon. Upstream of the yopE gene, 620 base pairs were conserved in the three species. This region contained a 130-amino-acid-long open reading frame reading in the opposite direction to the yopE gene and expressed a 14-kilodalton protein in minicells. An insertion mutation in this region constructed in Y. pseudotuberculosis expressed significantly lower amounts of YopE protein in vitro than did the corresponding wild type. The expression level could be restored by transcomplementation. This new locus was designated yerA, for yopE-regulating gene A. The yerA mutant was avirulent when mice were challenged by oral infection.

A synthetic oligonucleotide probe and a cloned polynucleotide probe based on the yopA gene for detection and enumeration of virulent Yersinia enterocolitica

We compared a synthetically produced 19-mer oligonucleotide probe with a polynucleotide probe consisting of a cloned fragment of the virulence gene yopA for their relative efficiencies in identification and enumeration of virulent Yersinia enterocolitica. The probes were used in DNA-DNA colony hybridization assays to differentiate 70 Yersinia strains with known plasmid profiles. All 19 strains harboring the 40- to 50-megadalton virulence plasmid were positive in the hybridization assay, whereas their isogenic derivatives lacking this plasmid were negative. Both probes correctly identified plasmid-bearing variants of Y. enterocolitica serogroups O:3, O:5,27, O:8, O:9, O:13, and O:21 from three continents. In contrast, none of the probes hybridized with DNA from 32 environmental yersiniae belonging to 26 serogroups not associated with disease. Colony hybridization was used to detect and enumerate virulent Y. enterocolitica in three artificially contaminated food samples. Despite a large background of indigenous bacteria (3 x 10(4) CFU), the efficiency of enumeration ranged from 33 to 82%. The use of nylon filters did not impair the growth of virulent yersiniae. Both probes showed a perfect concordance in their specific differentiation and enumeration of virulent Y. enterocolitica. DNA colony hybridization with these two probes permitted rapid and reliable identification of all common pathogenic serogroups without the need for enrichment or esoteric identification protocols.

Binding to collagen by Yersinia enterocolitica and Yersinia pseudotuberculosis: evidence for yopA-mediated and chromosomally encoded mechanisms

Binding of Yersinia enterocolitica and Yersinia pseudotuberculosis strains to type I, II, and IV collagens has been studied. Wild-type strains which harbored the 40- to 50-megadalton virulence plasmid specifically bound all three types of collagen. Curing of the virulence plasmid or Tn5 insertion in the yopA gene encoding the temperature-inducible outer membrane protein YOP1 abolished the binding of all three collagen types to Y. enterocolitica and type I and II collagens to Y. pseudotuberculosis. Full binding capacity was restored by introduction of the yopA gene into nonbinding Yersinia strains. Binding of type I, II, and IV collagens was expressed in Escherichia coli constructs harboring the yopA gene of either Y. enterocolitica or Y. pseudotuberculosis. The interaction of bacterial cells with type I collagen could be blocked by nonradiolabeled native collagens or denatured collagen but not with other serum and connective-tissue proteins. Unlabeled collagen could not displace bound radiolabeled collagen. The binding was inhibited by YOP1-specific polyclonal antibodies, in contrast to normal rabbit serum. The interaction was rapid and was quite resistant to heat treatment, to proteolytic enzymes, to various pHs in both acidic and alkaline ranges, and to the chaotropic agent urea. We propose that this newly identified interaction may be involved both in the first steps of the pathogenesis and in the complications of Yersinia infections affecting connective tissue.

Detection of cross-reacting epitopes on plasmid-encoded outer membrane proteins of enteropathogenic Yersinia by monoclonal antibodies

Plasmid-positive Yersinia bacteria of different species and different serotypes were analysed with respect to the immunological relationship of two of their plasmid-encoded outer membrane proteins (OMPs) by the immunoblot technique using three monoclonal antibodies (mAb), which were induced against OMPs of Yersinia enterocolitica serotype O:9 bacteria. Evidence is presented that these OMPs display discrete epitopes, which are common to all plasmid-positive Yersinia strains tested, with only one exception, indicating a close structural relationship of the OMPs analysed.

Binding of Yersinia enterocolitica to rabbit intestinal brush border membranes, mucus, and mucin

Mucus and its gel-forming glycoprotein component, mucin, are thought to protect the gastrointestinal tract from enteric pathogens by inhibiting their attachment to enterocytes. In this study, we investigated interactions between Yersinia enterocolitica (isogenic strains of virulent and nonvirulent organisms) and crude mucus, highly purified mucin, and brush border membranes (BBMs) isolated from the upper mid-, and distal small intestine and the proximal colon of the rabbit. Adherence of radiolabeled bacteria was assessed to BBMs, mucus, and mucin immobilized in polystyrene microtiter plate wells. Virulent Y. enterocolitica showed saturable binding to mucus, mucin, and BBMs from all four regions of the intestinal tract, although adherence to BBMs was appreciably greater than that to mucus or mucin. Maximal binding of bacteria was higher to BBMs from the distal small intestine and the proximal colon than to those from the upper and mid-small intestine, which may in part explain why the organism localizes to the ileo-caecal regions of the gut. Adherence of virulent Y. enterocolitica to BBMs was significantly reduced in the presence of homologous mucus or mucin preparations. Binding of virulent bacteria appears to depend on plasmid-encoded proteins located on the outer surface membrane, since (i) the isogenic strain lacking the virulence plasmid showed markedly less binding to all BBM, mucus, and mucin preparations; (ii) growth of the virulent strain at 25 degrees C, which inactivates its plasmid, significantly diminished binding to BBMs, mucus, and mucin; and (iii) mild proteolysis substantially decreased adherence of virulent bacteria to BBMs. Compared with rabbit intestinal and colonic mucins, binding of virulent Y. enterocolitica was significantly greater to purified human intestinal mucin and significantly less to rat intestinal mucin. These findings provide support for the role of mucus and mucin in host defense by preventing adherence of virulent Y. enterocolitica to epithelial cell membranes.

Molecular analysis of lcrGVH, the V antigen operon of Yersinia pestis

The lcrGVH operon of plasmid pCD1 in Yersinia pestis KIM encodes the virulence-associated V antigen, the regulatory protein LcrH, and LcrG, a protein of undefined function. In this study we sequenced lcrGVH and analyzed it for transcription initiation sites. There were three open reading frames within the sequence, 288, 981, and 507 bases in length, which could encode proteins with molecular weights and isoelectric points corresponding to those of LcrG, LcrV (V antigen), and LcrH, respectively. The predicted LcrV protein lacked an N-terminal signal sequence; however, an internal signallike sequence was present. An Escherichia coli-like promoter consensus sequence was detected upstream from lcrG. Primer extension analysis showed that (i) the transcriptional start site for lcrGVH was spaced only three bases upstream from the nearest ATG potential start site, raising the possibility that Y. pestis may use an alternate initiation codon for the V operon; (ii) there was much more primer-extended product in yersiniae grown in the absence of Ca2+ than in its presence, showing for the first time that lcrGVH is regulated at the transcriptional level by Ca2+; (iii) no separate lcrV initiation was detected, indicating that the V antigen is expressed from messages initiating at lcrG; and (iv) a non-Ca2+-regulated transcriptional start site was found upstream from lcrH, suggesting that the LcrH protein is expressed constitutively. However, two-dimensional gel analysis showed that net LcrH expression was regulated by Ca2+. We propose that lcrH lies within two differentially regulated operons, its own and lcrGVH.

The yopM gene of Yersinia pestis encodes a released protein having homology with the human platelet surface protein GPIb alpha

In Yersinia pestis KIM, there are 11 Yops (yersinial outer membrane proteins) encoded by the low-Ca2+ response virulence plasmid pCD1. Only Yops M and N are found in easily detectable amounts in the culture medium. In this study, we located and characterized the yopM gene to obtain clues about its role in the virulence of Y. pestis. Rabbit antibody was raised against Yops M and H, copurified from the supernatant of Y. pseudotuberculosis 43(pGW600, pCD1 yopE::Mu dI1[Apr lac]). This antiserum was adsorbed with an Escherichia coli clone that strongly expressed YopH. The resulting YopM-specific antibody was used to screen a HindIII library of pCD1. HindIII-F and several subclones from it expressed YopM in E. coli minicells. A DNA fragment of 1.39 kilobases from HindIII-F was sequenced and found to contain a 367-amino-acid open reading frame capable of encoding a protein with molecular mass (41,566 daltons) and isoelectric point (4.06) similar to those of YopM. The +1 site of the yopM gene was determined by primer extension. The DNA sequence contained repeating structures: 11 pairs of exact direct repeats, two exact inverted repeats, and three palindromes, ranging from 10 to 42 bases in size. One consensus 14-amino-acid sequence was repeated six times in the predicted protein sequence. The YopM sequence shares some significant homology with the von Willebrand factor- and thrombin-binding domain of the alpha chain of human platelet membrane glycoprotein Ib. These findings suggested a testable hypothesis for the function of YopM.

Influence of nutrient-limited growth on pathogenesis-associated outer membrane proteins of Yersinia enterocolitica

From studies based on batch culture, it has been postulated that the expression of the virulence-associated proteins of Yersinia spp. is controlled by temperature and Ca2+, such that these proteins are synthesized only at the higher temperature (37 degrees C) and calcium-scarce conditions of the intracellular environment. It was found, however, that in Yersinia enterocolitica one of these proteins (140 kDa) is not synthesized at submaximal growth rates under any of the relevant conditions, and that another of the implicated proteins (34 kDa), is synthesized even at 28 degrees C during nutrient-limited growth. Thus, temperature and Ca2+ influence the synthesis of these proteins differently under growth conditions that better approximate the natural environments than do batch cultures.

Thermoregulation-dependent expression of Yersinia enterocolitica protein 1 imparts serum resistance to Escherichia coli K-12

Resistance to the bactericidal action of normal human serum is one of the characteristics of virulent Yersinia enterocolitica. This property is attributable to the virulence plasmid harbored by pathogenic strains of the species. Serum resistance in Y. enterocolitica is thermoregulated, and its expression correlates well with the presence of virulence plasmid-encoded outer membrane proteins. To further examine the biochemical basis underlying resistance, we cloned a large segment (ca. 30 kilobases) of virulence plasmid DNA and studied the expression of plasmid-encoded outer membrane proteins in a serum-sensitive strain of Escherichia coli. The presence of the 160-kilodalton Y. enterocolitica-derived outer membrane protein 1 on E. coli transformants conferred a high degree of hydrophobicity, autoagglutinability, and resistance to serum killing. All of these properties were thermoregulated in E. coli with fidelity, suggesting that a functional thermoregulatory element was present in the cloned DNA. Elimination of protein 1 from the outer membrane of E. coli transformants by insertional inactivation of the structural gene with a Kanr gene cassette abrogated all of these properties and returned the serum-sensitive phenotype.

Development and testing of a synthetic oligonucleotide probe for the detection of pathogenic Yersinia strains

A 24-base oligonucleotide probe specific for a region of the Yersinia enterocolitica virulence plasmid (pYV) associated with HEp-2 cell cytotoxicity and the Sereny reaction was constructed by using sequences flanking critical TnphoA insertions in a subcloned fragment of pYV. This probe, highly specific and sensitive for virulent yersiniae, detected pathogenic Y. enterocolitica isolates in artificially inoculated foods.

Determinants for thermoinducible cell binding and plasmid-encoded cellular penetration detected in the absence of the Yersinia pseudotuberculosis invasin protein

Yersinia pseudotuberculosis inv mutants were analyzed for their ability to bind and penetrate mammalian cell lines. Strains defective for the production of invasin and cured of the Yersinia virulence plasmid pIB1 were extremely defective for entry into the HEp-2 cell line. inv strains harboring the virulence plasmid partially overcame this defect, indicating that the virulence plasmid mediates an invasin-independent pathway for low-level entry into cultured cells. Plasmid-cured inv mutants were able to attach efficiently to mammalian cells after bacterial culture at 37 degrees C but not after culture at a lower temperature. The enhanced cellular binding of inv mutants grown at 37 degrees C did not result in efficient cellular penetration, indicating that invasin-mediated entry is the primary chromosomally encoded pathway responsible for Y. pseudotuberculosis penetration into both HEp-2 and Chinese hamster ovary cells under the assay conditions described here.

Immunoblot analysis of IgM, IgG, and IgA responses to plasmid encoded released proteins of Yersinia enterocolitica in patients with or without yersinia triggered reactive arthritis

The IgM, IgG, and IgA antibody responses of patients with Yersinia enterocolitica O:3 infection were studied by immunoblotting with plasmid encoded released proteins of Y enterocolitica as the antigens. The results indicate that antibodies of all three classes are most consistently directed against the proteins of molecular weights 25,000 and 36,000. Less than two months after the onset of infection 18 of the 19 patients with yersinia triggered reactive arthritis had IgA class antibodies against the released protein of mol. wt 36,000, whereas only eight of the 17 patients with non-arthritic yersiniosis had these antibodies. The same difference between the arthritic and non-arthritic patients was observed also 8-12 months after the onset of infection.

A Yersinia pestis-specific DNA fragment encodes temperature-dependent coagulase and fibrinolysin-associated phenotypes

The effect of temperature on coagulase and fibrinolysin expression (Pla) by Yersinia pestis has been implicated in the transmission of plague by fleas. In an attempt to improve our understanding of this process, we have cloned, sequenced and characterized the gene encoding the Pla phenotypes in Y. pestis, and examined its temperature-dependent regulation. The coding region for this gene overlaps a 900bp Y. pestis-specific DNA fragment that we have previously shown to be capable of detecting plague bacilli in fleas. The pla gene contains a single open reading frame encoding 312 amino acids with a predicted molecular weight of 34.7 kD and a putative signal sequence of 20 amino acids. This coding region appears to be sufficient for both coagulase and fibrinolytic activities. In Y. pestis, modulation between coagulase and fibrinolytic activities is temperature-dependent: coagulase activity is most evident at temperatures below 30 degrees C but fibrinolytic activity increases with higher temperatures (greater than 30 degrees C), regardless of the temperature at which the bacteria are grown. Our results lead us to believe that this regulation occurs post-translationally. It is possible that the alternative forms of the Pla protein are essential to 'flea blockage' and subsequent transmission of the plague bacillus to animals.

Expression of gonococcal protein II in Escherichia coli by translational fusion

A protein II (P.II) gene from Neisseria gonorrhoeae was cloned in Escherichia coli and characterized by DNA sequence analysis. As with other reported P.II sequences, this gene contains an ATG initiation codon which is out of frame with respect to the remainder of the P.II amino acid sequence. A translational fusion was constructed in E. coli which linked the P.II sequence to the signal peptide of beta-lactamase. This P.II fusion differs from the gonococcal protein only in the first seven residues at the N terminus. In E. coli, the P.II fusion product exhibits properties analogous to those of P.II in N. gonorrhoeae. The P.II fusion product is a major component of the E. coli outer membrane and it is exposed on the cell surface. The P.II fusion protein also exhibits the heat-modifiable phenotype of gonococcal P.II.

lcrH, a gene necessary for virulence of Yersinia pestis and for the normal response of Y. pestis to ATP and calcium

We are investigating the functions of the three proteins encoded by the V operon (lcrGVH) of the low-calcium response virulence plasmid pCD1 of Yersinia pestis KIM5. The purpose of this study was to define the role of the 18-kilodalton protein encoded by lcrH, the third gene of the V operon. Using marker exchange mutagenesis, we constructed a Y. pestis mutant that failed to express the LcrH protein. This LcrH- mutant was "ATP blind" in that it failed to show altered growth and V-antigen expression at 37 degrees C when 18 mM ATP was present. It also showed only a partial response to 2.5 mM Ca2+. The parental Y. pestis strain showed full growth yield at 37 degrees C and depressed expression of V antigen and of yop (yersinial pCD1-encoded outer membrane protein) genes in response to ATP or Ca2+. In contrast, the LcrH- mutant failed to grow at 37 degrees C in the presence of ATP and showed only limited growth when Ca2+ was present. V-antigen expression in the mutant was not depressed by ATP and only partially depressed by Ca2+. These findings show that LcrH is necessary for the normal response of Y. pestis to ATP and that LcrH contributes to Ca2+ responsiveness. The mutant also showed abnormal yopJ expression, indicating that LcrH also is necessary for normal yop regulation. The LcrH- mutant was avirulent in mice, probably because of its compromised growth at 37 degrees C. These findings indicate that the responses of Y. pestis to ATP and Ca2+ are distinct and that lcrH encodes a protein that is an important mediator of Ca2+ and ATP regulation of pCD1-encoded virulence determinant(s) in Y. pestis.

Serum opsonic capacity against Yersinia enterocolitica O:3 in yersiniosis patients with or without reactive arthritis

The opsonic capacity of 45 sera from patients with reactive arthritis after Yersinia enterocolitica O:3 infection and of 45 matched sera from yersiniosis patients without post-infection complications was studied at 1-3 months, 5-8 months and 12-20 months after the onset of the infection. Antibody-mediated opsonization of virulence-plasmid-containing Y. enterocolitica O:3 was studied by measuring complement-fixation on opsonized bacteria and opsonophagocytic function of the polymorphonuclear leucocytes (PMN). The PMN response against bacteria pre-opsonized by heat-inactivated sera was measured by using a chemiluminescence (CL) assay. The fixation of complement Clq and C3 on bacteria was determined by flow cytometry using fluorescein-conjugated Clq- and C3c-antisera. All the sera were strongly opsonic at the onset of the infection, and this capacity persisted in most of the patients still at the end of the follow-up. No difference was observed in complement-fixing capacity between the sera of the two groups, but the sera from arthritic patients showed stronger augmentation of PMN CL response at the early phase of the infection (P = 0.005 in the presence of complement, P = 0.04 in the absence of complement). These results suggest that enhanced opsonic capacity may play a role in the development of Yersinia-triggered reactive arthritis by leading to strong activation of the PMN and, consequently, to release of inflammatory mediators.

Production of bacteriocin-like antagonism by clinical isolates of Yersinia enterocolitica

Fourteen clinical isolates of Yersinia enterocolitica serotype O:3 and four well-documented virulent strains of serotypes O:3, O:8, and O:9 were biotyped and examined for plasmid-associated autoagglutination and calcium dependency and for epithelial cell adherence. These strains were tested for the production of bacteriocin-like antagonism by using tryptone soya blood agar at room temperature and at 37 degrees C. By using the cross-streaking method, three clinical isolates produced inhibitory substances at room temperature. These substances were active against a variety of clinical isolates and their plasmid-cured derivatives at both room temperature and 37 degrees C. The inhibition was easier to read after incubation of the cross-streaked plate at 37 degrees C. The inhibition patterns indicate that two of the three producer strains appear to recognize potentially virulent O:3 strains, with or without the virulence plasmid.

Evaluation of enzyme immunoassay for the detection of pathogenic Yersinia enterocolitica and Yersinia pseudotuberculosis strains

To determine the virulence plasmid-harboring strains of Yersinia enterocolitica, we prepared antiserum against plasmid-encoded proteins of Y. enterocolitica serotype O3 and carried out an enzyme immunoassay (EIA) against temperature-inducible released proteins. This serum reacted with proteins released from not only a Y. enterocolitica serotype O3 strain but also Y. enterocolitica serotype O5:27, O8, and O9 and Y. pseudotuberculosis serotype 1b, 2a, 2b, 2c, 3, 4a, 4b, 5a, 5b, 6, 7, and 8 strains, which all harbored plasmids. Plasmid-cured Y. enterocolitica and Y. pseudotuberculosis strains did not react in the EIA, nor did nonpathogenic Y. enterocolitica strains or Y. frederiksenii, Y. intermedia, and Y. kristensenii strains. These observations demonstrated that this EIA was useful for determining whether the isolated Yersinia strains were pathogenic or not.