Plasmids in Yersinia enterocolitica serotypes O:3 and O:9: correlation with epithelial cell adherence in vitro

Identification of distinct lipopolysaccharide patterns among Yersinia enterocolitica and Y. enterocolitica-like bacteria

The lipopolysaccharide (LPS) of strains representing various serotypes of Yersinia enterocolitica and Y. enterocolitica-like bacteria was studied by deoxycholate-PAGE and silver staining analysis. Four main types of LPS were detected based on the O-polysaccharide (O-PS): (i) LPS with homopolymeric O-PS, (ii) LPS with ladder-forming heteropolymeric O-PS, (iii) LPS with single-length O-PS, and (iv) semi-rough LPS without O-PS. Within the first three types, several subvariants were detected. Selected serotypes representing all above LPS types are sensitive to bacteriophage φR1-37 indicating that they share the phage receptor, a hexasaccharide called outer core in Y. enterocolitica O:3. Whereas phage φR1-37-resistant mutants of homopolymeric O-PS have lost only the outer core, those of ladder-forming or single-length O-PS have lost also the O-PS suggesting that in the latter ones the outer core is bridging between O-PS and lipid A-core. This work forms a basis of further structural, biochemical and genetic studies of these LPSs.

Yersinia enterocolitica: Mode of Transmission, Molecular Insights of Virulence, and Pathogenesis of Infection

Although Yersinia enterocolitica is usually transmitted through contaminated food and untreated water, occasional transmission such as human-to-human, animal-to-human and blood transfusion associated transmission have also identified in human disease. Of the six Y. enterocolitica biotypes, the virulence of the pathogenic biotypes, namely, 1B and 2-5 is attributed to the presence of a highly conserved 70-kb virulence plasmid, termed pYV/pCD and certain chromosomal genes. Some biotype 1A strains, despite lacking virulence plasmid (pYV) and traditional chromosomal virulence genes, are isolated frequently from humans with gastrointestinal diseases similar to that produced by isolates belonging known pathogenic biotypes. Y. enterocolitica pathogenic biotypes have evolved two major properties: the ability to penetrate the intestinal wall, which is thought to be controlled by plasmid genes, and the production of heat-stable enterotoxin, which is controlled by chromosomal genes.

Functional mapping of YadA- and Ail-mediated binding of human factor H to Yersinia enterocolitica serotype O:3

Yersinia enterocolitica is an enteric pathogen that exploits diverse means to survive in the human host. Upon Y. enterocolitica entry into the human host, bacteria sense and respond to variety of signals, one of which is the temperature. Temperature in particular has a profound impact on Y. enterocolitica gene expression, as most of its virulence factors are expressed exclusively at 37 degrees C. These include two outer membrane proteins, YadA and Ail, that function as adhesins and complement resistance (CR) factors. Both YadA and Ail bind the functionally active complement alternative pathway regulator factor H (FH). In this study, we characterized regions on both proteins involved in CR and the interaction with FH. Twenty-eight mutants having short (7 to 41 amino acids) internal deletions within the neck and stalk of YadA and two complement-sensitive site-directed Ail mutants were constructed to map the CR and FH binding regions of YadA and Ail. Functional analysis of the YadA mutants revealed that the stalk of YadA is required for both CR and FH binding and that FH appears to target several conformational and discontinuous sites of the YadA stalk. On the other hand, the complement-sensitive Ail mutants were not affected in FH binding. Our results also suggested that Ail- and YadA-mediated CR does not depend solely on FH binding.

Characterization of complement factor H binding to Yersinia enterocolitica serotype O:3

A number of bacteria bind factor H (FH), the negative regulator of the alternative complement pathway, to avoid complement-mediated killing. Here we show that a gram-negative enteric pathogen, Yersinia enterocolitica serotype O:3, uses two virulence-related outer membrane (OM) proteins to bind FH. With Y. enterocolitica O:3 mutant strains displaying different combinations of surface factors relevant to complement resistance, we demonstrated that the major receptor for FH is the OM protein YadA. Another OM protein, Ail, also contributes to FH binding provided that it is not blocked by distal parts of the lipopolysaccharide (i.e., the O antigen and the outer core hexasaccharide). Importantly, we demonstrated that surface-bound FH was functional; both YadA- and Ail-bound FH displayed cofactor activity for factor I-mediated cleavage of C3b. With truncated recombinant FH constructs, we located the binding site of Ail specifically to short consensus repeats 6 and 7 of FH, while YadA showed a novel type of FH-binding pattern and appears to bind FH throughout the entire FH molecule. We thus conclude that Y. enterocolitica, via YadA and Ail, recruits functionally active FH to its surface. FH binding appears to be an important mechanism of the complement resistance of this pathogen.

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.

Note: inhibition of the growth of Yersinia enterocolitica O:3 by the microflora of porcine caecum and ileum in an in vitro model

The growth of Yersinia enterocolitica O:3 was tested in an in vitro model of the porcine intestine at the physiological temperature of 39 degrees C of growing pigs. The model supported a stable population of Y. enterocolitica at a level 10(8)-10(9) cells ml-1. Plasmid profile analysis and the Ca(2+)-dependent proportion of the population suggested that the great majority of the Y. enterocolitica population retained the 70 kb virulence plasmid, pYV, throughout the experimental period of 5 d. The growth of Y. enterocolitica was substantially inhibited by the ileal and the caecal flora compared to the growth of the bacterium alone. Yersinia enterocolitica was not isolated after 3 d of cultivation.

Role of iron in pathogenesis of guinea pigs infected with Yersinia enterocolitica 0:3

Examined have been the pathogenesis of guinea pigs preliminarily overload with iron, and infected with Yersinia enterocolitica 0:3 in a logarithmic and stationary phase of development, cultivated at 25 degrees C and 37 degrees C. Dextrofer-100 (Fedex-100) medicine have been used as an iron source. The results show that in spite of the phase of development and cultivation temperature, the iron excess does not increase the bacterial virulence of the strain used so far. The morphological changes in the mesenterial lymphatic nodes, small intestines, spleen and liver of guinea pigs treated with iron, and then, infected with Y. enterocolitica, are more slightly expressed as compared with animals infected with Y. enterocolitica only. The investigations suggested so far, have attested that Yersinia enterocolitica 0:3 does not contain a gene responsible for the synthesis of the protein participating in iron uptake.

Yersinia frederiksenii infection and colonization in hospital staff

A diagnosis of gastrointestinal infection with Yersinia frederiksenii was made in a 24-year-old female hospital doctor, resident in hospital. An additional three of nine medical residents screened were found to be faecal carriers of Y. frederiksenii. The latter three residents denied any gastrointestinal symptoms. Screening of 25 resident nurses and 25 in-patients for carriage of Y. frederiksenii was negative. Initial investigation revealed that the medical residents frequently drank unpasteurized milk, which was supplied on the understanding that it would be used for cooking only. Counts of > 10(8) cfu l-1 were obtained from unpasteurized milk samples, including 24 species of Gram-negative bacilli. Yersinia spp. were not isolated. Residents also drank water from the cold taps in the bedrooms; this water was supplied by a holding tank on the hospital roof. Subsequent investigations revealed that three of the 21 holding tanks supplying stored water to the hospital were not covered. Y. enterocolitica was isolated from the uncovered water tank supplying the medical residence.

Amino acid substitutions in naturally occurring variants of ail result in altered invasion activity

Yersinia enterocolitica is the causative agent of a variety of gastrointestinal syndromes ranging from acute enteritis to mesenteric lymphadenitis. In addition, systemic infections resulting in high mortality rates can occur in elderly and immunocompromised patients. More than 50 serotypes of Y. enterocolitica have been identified, but only a few of them commonly cause disease in otherwise healthy hosts. Those serotypes that cause disease have been divided into two groups, American and non-American, based on their geographical distributions, biotypes, and pathogenicity. We have been studying two genes, inv and ail, from Y. enterocolitica that confer in tissue culture assays an invasive phenotype that strongly correlates with virulence. Some differences between the American and non-American serotypes at the ail locus were noted previously and have been investigated further in this report. The ail locus was cloned from seven Y. enterocolitica strains (seven different serotypes). Although the different clones produced similar amounts of Ail, the product of the ail gene from non-American serotypes (AilNA) was less able to promote invasion by Escherichia coli than was the product of the ail gene from American serotypes (AilA). This difference is probably due to one or more of the eight amino acid changes found in the derived amino acid sequence for the mature form of AilNA compared with that of AilA. Seven of these changes are predicted to be in cell surface domains of the protein (a model for the proposed folding of Ail within the outer membrane is presented). These results are discussed in relation to the growing family of outer membrane proteins, which includes Lom from bacteriophage lambda, PagC from salmonella typhimurium, and OmpX from Enterobacter cloacae.

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.

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.

Sequence, localization and function of the invasin protein of Yersinia enterocolitica

The inv locus of Yersinia enterocolitica is sufficient to convert a non-invasive Escherichia coli K12 strain into a microorganism that is able to penetrate cultured mammalian cells. The nucleotide sequence of inv reveals an open reading frame corresponding to an 835-amino-acid protein that is homologous to the invasin protein from Yersinia pseudotuberculosis. A polyclonal antiserum elicited by a synthetic peptide corresponding to the C-terminal 88 amino acids of this open reading frame detected a unique 100 kD protein in cell lysates of Y. enterocolitica strain 8081 c and in an E. coli strain harbouring the cloned inv gene. This protein localized to the outer membranes of both microorganisms and was cleaved by low concentrations of extracellular trypsin. HEp-2 cells were shown to attach to surfaces coated with bacterial outer membranes containing invasin and this attachment was destroyed by treatment of the membranes with trypsin. Thus it appears that the invasin protein from Y. enterocolitica is able to mediate both attachment to and entry of cultured epithelial cells.

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.

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.

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

The Yop proteins of Yersinia are important virulence determinants. The Yop1 protein sequences of Yersinia pestis, Yersinia pseudotuberculosis, and two Yersinia enterocolitica serotypes, 0:3 and 0:8, deduced from the nucleotide sequences of the corresponding yopA genes, were compared. Most differences were found in the hydrophilic domains of the proteins, whereas the hydrophobic domains were conserved. The amino acid sequences revealed a signal sequence 25 amino acids long. No cysteine residues were present, even though Yop1 forms a polymeric structure. The transcription startpoint of yopA was determined by primer extension. The coding region and transcription startpoint were separated by a leader sequence 270 nucleotides long. The yopA promoter sequence of Y.pestis is identical to the corresponding sequence of Y. pseudotuberculosis and transcription studies revealed that this promoter is active in Y.pestis. Thus, the inability of Y.pestis to express the Yop1 protein is due to a single base pair deletion in the coding region of the yopA gene of Y.pestis.

The ail locus is found uniquely in Yersinia enterocolitica serotypes commonly associated with disease

Yersinia enterocolitica is a heterogeneous group of organisms with more than 50 serotypes and several biotypes. Only a few of these serotypes cause gastrointestinal disease in otherwise healthy hosts; these serotypes are the pathogenic serotypes. Although Y. enterocolitica requires a high-molecular-weight plasmid to cause disease, chromosome-encoded determinants are required for the full expression of virulence. The ability of Yersinia spp. to invade eucaryotic cells is thought to be a virulence factor, because nonpathogenic serotypes are noninvasive in animals and in tissue culture cell models. Current evidence indicates that invasion ability is chromosome encoded. We recently reported cloning two loci, inv and ail, from Y. enterocolitica O8 strain 8081c that allow Escherichia coli to invade tissue culture cells. We investigated the link between invasion in an in vitro tissue culture invasion (TCI) model and hybridization to probes derived from the two invasion loci, inv and ail. We examined 177 Yersinia strains. Strains of serotypes and species associated with disease were TCI+, whereas strains of serotypes and species not associated with disease were TCI-. Only TCI+ strains had DNA homologous to probes derived from ail. All strains (TCI+ and TCI-) had DNA homologous to probes derived from inv, but there were certain restriction fragment-linked polymorphisms that were associated primarily with TCI+ strains. These observations held true for strains epidemiologically associated with disease. Both the inv and ail loci were found to be clearly located on the chromosome. No other genera, including other invasive organisms, had DNA homologous to inv or ail. These data support the hypothesis that the ail locus encodes a Y. enterocolitica invasion factor that may be involved in pathogenesis.

Intact motility as a Salmonella typhi invasion-related factor

Invasiveness of Salmonella typhi was investigated. At first, we introduced Tn5 into the chromosome of a wild-type S. typhi strain, GIFU 10007, and screened the independent Tn5 insertion mutants for noninvasive (Inv-) strains. During the first half of this work, we obtained 4 Inv- strains from 1,338 independent Tn5 mutants. The four were either nonflagellate (Fla-), nonmotile (Mot-), or nonchemotactic (Che-). We then isolated more Fla-, Mot-, or Che- mutants and examined the invasiveness of these mutants. Sixty-three spontaneous or Tn5 insertion motility mutants, i.e., Fla-, Mot-, or Che-, were independently isolated from the wild-type strain GIFU 10007; all of them were noninvasive. Motile revertants isolated from some of these mutants showed the same invasiveness as the parent strain. P22-mediated transductional crosses were carried out between some of the motility mutants (as the recipients) and the Fla- reference strains of S. typhimurium with known deletion sites on the genome (as the donors). The mutational sites of the S. typhi mutants were assigned almost evenly to the three flagellar gene regions (regions I, II, and III) of S. typhimurium. The invasiveness of the motile recombinants obtained from the transduction assays was examined. The restoration of intact motility resulted in the restoration of invasiveness. Thus, we conclude that intact motility is an invasion-related factor of S. typhi. The relationship of Vi antigen to the invasiveness of S. typhi was also studied. Vi-negative mutants with intact motility remained invasive, whereas all 63 Inv- spontaneous or Tn5 mutants were Vi positive. Therefore, Vi antigen was not related to the invasiveness of S. typhi.

Evidence for two genetic loci in Yersinia enterocolitica that can promote invasion of epithelial cells

Virulent strains of Yersinia enterocolitica cause disease syndromes ranging from mild gastroenteritis to lymphadenitis and septicemia. The ability of these bacteria to invade intestinal epithelial cells to gain access to the reticuloendothelial system is thought to be an important aspect of their virulence. We report here on the cloning of two Y. enterocolitica chromosomal loci, inv and ail, each of which confers an invasive phenotype on Escherichia coli HB101. The inv locus allows a uniformly high level of invasion in several tissue culture lines and is homologous to the inv gene of Yersinia pseudotuberculosis. The second locus, ail, shows more host specificity than inv in that it allows invasion to a variable degree of some cell lines (e.g., HEp-2, HEC1B, and CHO cells) but allows no invasion of others (e.g., Madin-Darby canine kidney cells).

Role of antibodies in the opsonization of Yersinia spp

We have determined the opsonic capacity of specific antibodies in patient sera obtained after Yersinia infection. The results indicate that Yersinia antibodies lead to complement activation through the classical pathway, thus overcoming the inhibition of complement-mediated opsonization in the absence of specific antibodies provided by the virulence plasmid in Yersinia enterocolitica and Yersinia pseudotuberculosis. Further, antibodies against plasmid-encoded structures, the Yersinia outer membrane proteins (YOPs), are not necessary in this effect. This is indicated by two facts. (i) Monoclonal antibodies directed against the O polysaccharide of Y. enterocolitica O:3 are capable of opsonizing the plasmid-containing bacteria through C1q binding. (ii) Rabbit antisera show opsonic activity when obtained by immunization both with plasmid-containing Y. enterocolitica expressing the YOPs and a plasmid-cured variant not expressing these proteins.

Plasmids of Yersinia enterocolitica and Yersinia pseudotuberculosis: analysis with restriction endonucleases

The plasmids of Yersinia enterocolitica and Yersinia pseudotuberculosis tested differed in regard to the following aspect: there were some of a molecular size of 41 to 47 Mdal which could be correlated with autoagglutination of the host bacteria, and the others with a smaller size of 19 to 34 Mdal that lacked the capacity to code for autoagglutination. Analysis of both types of plasmids with the restriction endonucleases Bam HI, Eco RI and Hind III besides of some similarities revealed also considerable serogroup-specific differences in their DNA fragmentation pattern.

Characteristics of Yersinia enterocolitica isolated from children with diarrhea in Italy

Of 2,500 fecal samples collected from children with diarrhea in the province of Siena, 35 (1.4%) were found to be positive for Yersinia enterocolitica. Of the isolates, 94.2% belonged to biotype 4, serotype 0:3; 2.8% belonged to biotype 2, serotype O:9; and 2.8% belonged to biotype 1, serotype O:6. The in vitro pathogenicity tests showed that all but two isolates were calcium dependent and autoagglutinable and that all but one were also invasive in HEp-2 cell culture. As regards plasmid content, 32 of 33 biotype 4, serotype O:3 strains harbored a plasmid of 48 megadaltons and 1 strain also harbored a small plasmid of 2 megadaltons. The biotype 2, serotype O:9 strain harbored a plasmid of 42 megadaltons; one of the two strans lacking plasmids belonged to biotype 1, serotype O:6, and the other belonged to biotype 4, serotype O:3. Pyrazinamidase activity was positive only for the biotype 1, serotype O:6 strain. Esculin was hydrolyzed only by the biotype 1, serotype O:6 strain.

Yersiniosis as a gastrointestinal disease

Anti-yersinia antibodies were assessed in sera from 630 patients admitted to a department of surgery for acute abdominal disease, using an enzyme-linked immunosorbent assay (ELISA). In 21 patients a high concentration of yersinia antibodies confirmed recent yersinia infection. Eight patients had an appendicectomy performed; in all patients with antibodies against Y. enterocolitica 9 or Y. pseudotuberculosis IA a true appendicitis was found at operation. Two patients with Y. enterocolitica 3 antibodies had acute terminal ileitis and mesenterial lymphadenitis. In 4 patients a diagnosis of acute pancreatitis was established; 2 of these had cholecystitis. Two further patients had cholecystitis without pancreatic affection. Two patients had colonic diverticulitis, 1 with perforation. The results demonstrate that yersinia infection may commonly give rise to a variety of acute abdominal inflammations, and stress the importance of serological and bacteriological diagnostic procedures.

Immunochemical analysis of plasmid-encoded proteins released by enteropathogenic Yersinia sp. grown in calcium-deficient media

Enteropathogenic Yersinia sp. releases plasmid-associated proteins of low molecular mass (26-67 kilodaltons) at 37 degrees C. In this study, the optimum conditions for the release of proteins were assessed and the released proteins (RPs) were analyzed for the manner of release, immunochemical characteristics, and the location of the genes necessary for their synthesis. Protein release was strongly enhanced when growth media were markedly depleted of calcium ions by precipitation with oxalate or chelation with EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid]. RP yields were greatest when Yersinia spp. were in the exponential growth phase. The RPs appeared to be released from the Yersinia spp. by secretion rather than by pinching off of membrane vesicles, because the RPs did not sediment during high-speed centrifugation nor were they contaminated to any significant degree with lipopolysaccharide. Moreover, immunoblot analysis revealed only traces of protein species related to RPs within the outer membranes of plasmid-positive Yersinia spp. grown at 37 degrees C under calcium-restricted conditions. Immunoblot studies also showed that the RPs of Y. enterocolitica serotypes O:3, O:8, and O:9 and the RP of Y. pseudotuberculosis serotype I are highly cross-reactive. Finally, the immunoprecipitates of the products of minicells which harbor Yersinia plasmids were used to demonstrate that at least three proteins immunochemically related to the released fraction were plasmid encoded. These results suggest that at least three of the RPs may be related to or identical with previously described plasmid-encoded Yersinia outer membrane proteins.

Yersinia enterocolitica infection in resistant and susceptible strains of mice

We investigated natural resistance in mice to Yersinia enterocolitica, an enteric bacterial pathogen of humans, with a view to determine host genetic factors that are important in resistance. Most mouse strains studied (C3H/HeN, BALB/c, BALB.B, DBA/2, A, Swiss, and SWR) were highly susceptible to infection (50% lethal dose [LD50], 2 X 10(2) to 6 X 10(2) Y. enterocolitica administered intravenously [i.v.]). In contrast, C57BL/6 mice were highly resistant (LD50, 2 X 10(5) Y. enterocolitica administered i.v.). Resistance to i.v. Yersinia infection did not appear to be related to the Ity locus (which codes for resistance to Salmonella typhimurium and other pathogens) because Ityr mice (C3H/HeN, DBA/2, A, and SWR) were more susceptible to Y. enterocolitica than were Itys (C57BL/6) mice. In addition, because BALB.B mice (congenic to C57BL/6 mice at the H-2 locus) were susceptible, resistance was probably not H-2 linked. BALB/c X C57BL/6 F1 mice were intermediate in their resistance to Y. enterocolitica infection (LD50, 3 X 10(4) organisms administered i.v.), suggesting that resistance to Y. enterocolitica depends on a gene dosage affect or a resistance gene(s) interaction between susceptible and resistant parents. Further studies with C57BL/6 and BALB/c mice as prototype resistant and susceptible strains were undertaken. A time course study of Y. enterocolitica growth in various organs following i.v. infection revealed no strain difference in bacterial growth during the first 48 h of infection. Thereafter, however, C57BL/6 mice were capable of restricting Y. enterocolitica growth in all tissues (liver, lung, spleen, kidneys), whereas extensive bacterial proliferation occurred in BALB/c mice tissues. BALB/c mice were also more susceptible to oral Y. enterocolitica infection than were C57BL/6 mice, demonstrating increased mortality and greater numbers of bacteria in the Peyer's patches. Finally, whereas thymus-bearing C57BL/6 X BALB/c F1 mice were resistant to infection, athymic (nude) C57BL/6 X BALB/c F1 mice were susceptible. These studies provide a model to investigate natural immunity to enteric pathogens at mucosal surfaces, as well as provide the basis for clarifying the role of host genotype in Y. enterocolitica resistance.

Natural and recombinant interferons inhibit epithelial cell invasion by Shigella spp

The effect of natural and recombinant interferons (IFNs) on the abilities of Shigella flexneri, S. sonnei, and Salmonella typhimurium to invade different human and murine cells was examined. Pretreatment of cell monolayers with natural and recombinant IFNs reduced the number of Shigella-infected cells in a dose-dependent manner. Establishment of an anti-invasive cellular state was time dependent, requiring 10 h for 50% inhibition of bacterial invasion. The inhibitory effect of IFN was species specific, with human or murine IFN effective against homologous but not heterologous cells. Gamma IFN was slightly more potent than alpha IFN at inhibiting bacterial invasion. Inhibition of Shigella invasion was dependent on the challenge dose of bacteria. Little inhibition of invasion was seen when cells were pretreated with low concentrations of IFN and challenged with high multiplicities of infection of Shigella sp. In contrast to Shigella invasion, the maximum inhibitory effect of IFN on Salmonella invasion of cells was observed at low levels (5 to 50 U) of IFN. These results suggest that Shigella and Salmonella invasions occur at unique sites on eucaryotic cells or by different penetration mechanisms. More importantly, these data suggest that IFN may play a significant role in host defense against Shigella and Salmonella infections.

Serotype-related HEp-2 cell interaction of Yersinia enterocolitica

The ability of human clinical isolates of Yersinia enterocolitica to interact with HEp-2 cells was found to vary considerably between the serotypes O:3, O:8, and O:9. Although all three serotypes adhered initially to the cell surface, regardless of incubation temperature of the bacterial inoculum or presence of the 40- to 48-megadalton virulence plasmid, the ability to localize intracellularly was not uniformly expressed. By using a combined light optical method based on differential interference contrast and UV incident light microscopy, we found that in serotype O:3, resistance to internalization was dependent upon prior growth at 37 degrees C and carriage of the virulence plasmid; in serotype O:9, this property was plasmid dependent but not temperature dependent; in serotype O:8, it was constitutive. The ability of serotype O:3 to resist internalization was correlated with the expression of plasmid-associated fibrillae on the bacterial surface. No relationship between fibrillation and HEp-2 cell interaction was apparent for serotype O:8 or O:9. Serotypes O:8 and O:9, unlike the O:3 strains studied, associated with HEp-2 cells in greater number after cultivation at 22 degrees C than after cultivation at 37 degrees C. We failed to establish a correlation between the expression of surface fibrillae and the ability to evoke guinea pig conjunctivitis.

Yersinia enterocolitica septicemia: clinical and microbiological aspects

Septicemia is a rare but serious complication of infection with Yersinia enterocolitica (Y.e.). Seven cases of Y.e. septicemia are presented. Five of the patients had no underlying disease predisposing to septicemia. Five patients displayed recurrent episodes of septicemia, despite treatment with recommended doses of antibiotics to which the isolates were sensitive in vitro. One patient developed endocarditis which required surgical replacement of the aortic valve. Other clinical manifestations were arthritis, diverticulitis and pulmonary abscesses. The outcome was fatal to 3 elderly patients. The serological response to Y.e. was followed by tube agglutination and a diffusion-in-gel enzyme-linked immunosorbent assay. One patient, with a benign course of illness, had transient elevated Y.e. antibody titres, while the 3 cases with a protracted disease showed sustained antibody responses for 6-18 months. Blood isolates of Y.e. had ordinary virulence characteristics identical to fecal isolates and produced extracellular beta-lactamase. All isolates were sensitive in vitro to trimethoprim-sulfamethoxazole, mecillinam, piperacillin, cefotaxime, ceftazidime, chloramphenicol and gentamicin. The lowest MIC values were recorded for mecillinam. Full synergistic activity was demonstrated when mecillinam was combined with trimethoprim-sulfamethoxazole, cefuroxime or rifampicin.

Experimental intestinal infection of rats by Yersinia enterocolitica 0:3. A follow-up study with specific antibodies to the virulence plasmid specified antigens

Rats were infected by intragastric inoculation of Yersinia enterocolitica 0:3 grown at room temperature. The events of the first 6 days of the infection were followed by staining sections of small intestine using an immunoperoxidase method. The specific antibodies used were either rabbit antibodies to antigens of Y. enterocolitica, to the temperature-inducible antigens specified by the virulence plasmid (pYV) of Y. enterocolitica, or monoclonal antibody to the pYV-specified autoagglutination protein P1. In the course of the infection Y. enterocolitica organisms were detectable in the terminal ileum already 1 h after the challenge. By 1 h the pYV-specified temperature-inducible antigens were expressed in Y. enterocolitica both in the lumen of the intestine and in the intestinal tissues, which indicates that the activation of pYV in vivo was very rapid. Y. enterocolitica organisms which had penetrated into the lamina propria of the villi were rapidly removed by phagocytic cells. Later organisms were located intracellularly in the lamina propria, in Peyer's patches and in the regional lymph nodes. The terminal ileum was the most severely affected part of the small intestine.

Quantitation of HeLa cell monolayer invasion by Shigella and Salmonella species

A major determinant in the virulence of Salmonella and Shigella spp. is the ability of these organisms to invade epithelial cells of the gastrointestinal mucosa and multiply intracellularly. The invasion of cell culture monolayers is a convenient experimental system to evaluate eucaryotic cell penetration and is correlated with the potential of a strain to cause human disease. We have developed an agarose-L agar overlay technique which allows for the convenient quantitation of the number of infected tissue culture cells in a monolayer. Bacterial strains were introduced onto antibiotic-free HeLa cell monolayers. Infected monolayers were washed, and noninternalized bacteria were counterselected with kanamycin (50 micrograms/ml). The number of infected HeLa cells present was determined by overlaying the monolayer with distilled water-agarose (0.5 to 1.5%) followed by an equal volume of 2X L agar. Bacterial colonies formed over infected cells in 24 h at 37 degrees C, and wells were counted with a dissecting microscope under X2 power. Bacterial colonies were not observed with noninvasive variants of Shigella spp. To obtain countable wells (20 to 200 CFU) the multiplicity of infection or invasion times were adjusted. With a 90-min invasion time, the invasive potential of a strain was reflected by the multiplicity of infection needed to produce countable wells. The quantitation of bacterium-invaded cells by using standard bacteriological methods is a convenient and rapid method to evaluate the invasive potential of bacterial strains. Additionally, parameters essential for the invasive process can easily be investigated.

Role of virulence-associated plasmid in the uptake and killing of Yersinia pseudotuberculosis by resident macrophages

Resistance to phagocytosis of Yersinia pseudotuberculosis by mouse resident macrophages was investigated using a highly virulent plasmid-bearing strain and its low-virulent plasmid-free derivative. It was found that plasmid-bearing and plasmid-less bacteria did not resist the ingestion step nor inhibit the oxidative burst and phagolysosomal fusion in the peritoneal macrophages. These in vitro data were further confirmed by the study of bacterial survival in infected mice. Bacteria from plasmid-bearing and plasmid-free strains were similarly eliminated during the first hours of infection in the liver and in the peritoneal cavity. Our results therefore suggest that plasmid-mediated virulence is not related to the resistance to the bactericidal activity of fixed macrophages of the reticuloendothelial system during the early phase of infection, and that plasmid-encoded factors are expressed after a latency period by an unknown mechanism.

Pathogenesis of Yersinia-triggered reactive arthritis: immunological, microbiological and clinical aspects

When a patient develops reactive arthritis after Yersinia enteritis, the following conditions are often fulfilled: the patient is HLA-B27-positive; however, some B27-negative individuals develop severe arthritis and some positives do not, in the initial phase, the diarrhea is milder, the anti-Yersinia antibody response of IgG class is more vigorous and persists longer, the anti-Yersinia antibody response of IgA class is more vigorous and persists much longer, the anti-Yersinia antibodies of IgA1 and IgA2 subclass, those with J-chain and, especially, those with secretory piece are produced more vigorously, indicating local immunostimulation close to the intestinal epithelium, in the early phase, Yersinia-IgM immune complexes are found in the circulation, and the lymphocyte transformation response against not only Yersinia but also against other gram-negative enteric bacteria is weaker. When all these aspects are considered together a strong suspicion arises that the patients who are destined to develop reactive arthritis fail in their first line of defense against the invading organism when contracting a Yersinia enteritis. This may lead to persistence of the microorganism within the body, e.g., in the intestinal epithelium or in the mesenteric lymphoid tissues, maintaining a stimulus for a prolonged--apparently futile and perhaps harmful--antibody production. Finally, the initiating and decisive factor should not be forgotten: the Yersinia. Why and how it triggers the process is at present one of the enigmas of the pathogenesis of reactive arthritis.

Lack of correlation between plasmid-encoded outer membrane proteins and virulence of Yersinia enterocolitica

When various strains of Yersinia enterocolitica belonging to serovars 0:1,3, 0:3, 0:5,27, 0:9 and 0:Tacoma harbouring 44- to 47-Md plasmids, or their spontaneously cured isogenic pairs, were inoculated (i. v., with standardized inocula) into Swiss female mice, the kinetics of bacterial survival in the spleen were followed, revealing inoculum destruction within 15 days. With both strains Ye8081 and WA (0:8, harbouring a 42-Md plasmid), the kinetics of bacterial growth ended in the death of mice. The early spleen bacterial uptake was the same with all strains studied, whether plasmid-harbouring or plasmid-less derivatives. In this study, virulent strain Ye8081 and both low-virulent IP383 and Ye9576 were shown to synthesize antigenically related outer membrane polypeptides plasmid-encoded at 37 degrees C and previously considered as virulence determinants.

Pyrazinamidase activity in Yersinia enterocolitica and related organisms

Pyrazinamidase activity was tested in 381 Yersinia strains from various ecological and geographical origins and belonging to the following species: Y. enterocolitica (five biogroups), Y. intermedia, Y. frederiksenii, Y. kristensenii, Y. aldovae, Y. pseudotuberculosis, and Y. pestis. The pyrazinamidase test was negative (Pyz-) in all bioserogroups of Y. enterocolitica, in which is usually harbored the virulence plasmid, and was involved in human or animal diseases. Y. pseudotuberculosis and Y. pestis were also Pyz-. The more ubiquitous bioserogroups of Y. enterocolitica, without naturally occurring virulence plasmid, and related species were all Pyz+. Pyrazinamidase activity allowed the separation of the pathogenic North American Y. enterocolitica isolates from other nonpathogenic strains within biogroup 1. Similarly, environmental biogroups 3A and 3B were clearly distinguished from pathogenic biogroup 3. However, the pyrazinamidase test was not linked to the presence of the virulence plasmid itself and should not replace the pathogenicity tests to assess the actual virulence of an individual strain. This test proved to be a valuable tool to distinguish potential pathogenic from nonpathogenic strains of Y. enterocolitica in epidemiological surveillance programs.

Outer membrane proteins and plasmids in different Yersinia enterocolitica serogroups isolated from man and animals

Human clinical isolates of Yersinia enterocolitica (serogroups 0:3, 0:8, and 0:9) harboured a 40-45 megadaltons plasmid, which was shared by strains isolated from cases of yersiniosis in animals (0:2 and 0:5) and from healthy swine (0:3 and 0:9). Possession of such plasmids was invariably correlated with expression of three temperature-regulated characteristics related to the bacterial surface: when cultivated at 37 degrees C, all plasmid-bearing strains, unlike their plasmid-cured mutants, (i) underwent autoagglutination, (ii) produced a distinct mannose-resistant haemagglutinin, and (iii) simultaneously synthesized ancillary outer membrane proteins (OMPs). None of these characters was expressed phenotypically at 22 degrees C. Dominant among the plasmid-associated, temperature-regulated OMPs was a high molecular weight protein of approximately 180 kilodaltons, which was found in strains of five different serogroups (0:2, 0:3, 0:5, 0:8, and 0:9) regardless of the source of isolation. Strains isolated from diseased animals and from healthy swine were quite similar, if not identical, to human clinical isolates with respect to these ancillary OMPs. In contrast to the plasmid-associated OMPs expressed only at 37 degrees C, a number of plasmid-independent OMPs were produced mainly at 22 degrees C.

Expression of antigens encoded by the virulence plasmid of Yersinia enterocolitica under different growth conditions

The expression of polypeptides of the virulence plasmid of Yersinia enterocolitica serotype O:3 was studied with the immunoblotting technique and specifically absorbed antisera to Y. enterocolitica O:3. At least 16 polypeptides were apparently specified by the virulence plasmid when plasmid-bearing bacterial were grown at 37 degrees C or intraperitoneally in semipermeable capsules. The different growth media used (also with added Ca2+) had quantitatively or qualitatively only a little influence on the expression of these polypeptides, whereas the growth temperature had a stronger influence. The best expression was achieved at 37 degrees C, at 22 degrees C the expression was weak, and at 4 degrees C the plasmid genes were inactive. Two chromosomally encoded polypeptides were expressed only at 37 degrees C, whereas the expression of eight polypeptides expressed at 22 degrees C was repressed at 37 degrees C. The intraperitoneal growth in capsules was used to detect the virulence plasmid-associated polypeptides of Yersinia pestis. Four plasmid-associated polypeptides were detected in Y. pestis with antiserum to Y. enterocolitica virulence plasmid antigens, and three were detected with antiserum to Y. pestis EV76. These results suggested that the virulence plasmid of Y. pestis was activated in the interstitial environment in vivo, where Ca2+ concentration was high, and also that the virulence plasmids of Y. enterocolitica and Y. pestis have three to four immunologically related polypeptides in common.

Enterotoxin production at 4, 22, and 37 degrees C by Yersinia enterocolitica and Yersinia enterocolitica-like bacteria isolated from porcine tonsils and pork products

Altogether, 71 strains of Yersinia enterocolitica and Yersinia enterocolitica-like bacteria from porcine tonsils and pork products were examined for their ability to produce enterotoxin using the infant mouse assay. Of these, 37 strains (52.1 %) produced enterotoxin at 22 °C, 3 were positive at 4 and 22 °C, and 1 was enterotoxigenic at 22 and 37°C. No strain was positive at all 3 temperatures. The highest prevalence of enterotoxin production at 22°C was detected in serotype 0:11 (80.0%), followed by 0:3/ biotype 4 (74.2 %), and 0:12 (66.7 %). Enterotoxin production at 4°C was recorded in 2 (15.4 %) of the Yersinia kristensenii strains (0:11, 0:12) and 1 of the Yersinia enterocolitica strains, (0:3) examined. One Yersinia kristensenii strain (0:11) was enterotoxigenic at 37 °C. The results indicate that enterotoxin production is a common feature of yersiniae isolated from porcine tonsils and pork products in Norway and may represent a possible source of food borne intoxication.

Role of the virulence-associated plasmids of Yersinia enterocolitica on its immunogenicity against Y. pestis

Forty-two strains selected from various serovars of Yersinia enterocolitica were studied for their ability to induce cross-protection against Y. pestis. Only primo-infected mice (i.v.) with inocula prepared from strains of Y. enterocolitica belonging to serovars 0:3, 0:9 and 0:5, 27 harbouring a 47-Mdal virulence-associated plasmid were resistant to Y. pestis. The spontaneously cured (plasmid-less) derivatives of these strains had lost the capacity to induce this cross-immunity.

Genetically manipulated virulence of Yersinia enterocolitica

Mobilizable virulence plasmids of Yersinia enterocolitica of serotypes O:3 and O:9 were constructed by cointegration of a mobilizable vector into the virulence plasmids. The obtained cointegrates were mobilized into plasmidless Y. enterocolitica strains of serotypes O:3, O:5, O:8, and O:9. The transfer experiments revealed the existence of two different subgroups of plasmid-associated traits. (i) Animal virulence functions (mouse lethality and conjuctivitis provocation) were only transferable to plasmid-cured derivatives of virulent parent strains (serotypes O:3, O:8, and O:9), but they were not transferable to Y. enterocolitica antigen reference strains (serotypes O:3 and O:8) or to a plasmidless clinical isolate of serotype O:5. A further striking result was that a serotype O:8 strain regained the mouse lethality trait after receipt of a plasmid from a strain not lethal to mice. These results demonstrate that plasmid-mediated animal virulence functions are not uniformly expressed within Y. enterocolitica. (ii) The second subgroup of plasmid-mediated traits (calcium dependency, surface agglutinogens, HEp-2 cell adherence, and protein release) were transferable to all Y. enterocolitica recipient strains tested (serotypes O:3, O:5, O:8, and O:9 of different origin). For the first time HEp-2 cell adherence and temperature-induced release of five major protein species are described as transferable traits.

Comparison of three tests for virulent Yersinia enterocolitica

Magnesium oxalate agar was found to select against virulent types of Yersinia enterocolitica. Small colonies isolated from magnesium oxalate agar which were presumably virulent generally contained no detectable virulence-specific plasmids, did not agglutinate with virulence-specific antiserum, and exhibited various degrees of virulence in mice. Results indicate that the virulence potential of a Y. enterocolitica isolate cannot always be identified by these in vitro methods and suggest that virulence also involves other factors yet to be identified.

A restriction map of virulence plasmid pVYE439-80 from a serogroup 9 Yersinia enterocolitica strain

A restriction map of the virulence plasmid pVYE439-80, isolated from Yersinia enterocolitica 439-80 (serogroup 9) was constructed for EcoRI, BamHI, SstII, and SmaI. The mapping was done after cloning of about two-thirds of the plasmid in Escherichia coli. The restriction pattern was compared to those obtained with plasmids isolated from Y. enterocolitica strains of serogroups 1, 3, and 5b. The restriction sites are particularly conserved in a region of about 25 kb. This region contains fragments that are also conserved in serogroup 8 strains [J. Heeseman, C. Keller, R. Morawa, N. Schmidt, H. J. Siemens, and R. Lauf (1983) J. Infect. Dis. 147, 107-115] and that were shown, in strains from this serogroup, to encode calcium dependency [D. A. Portnoy, H. Wolf-Watz, I. Bolin, A. B. Beeder, and S. Falkow, (1984) Infect. Immun. 43, 108-114].