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

Microbial evolution and transitions along the parasite-mutualist continuum

Virtually all plants and animals, including humans, are home to symbiotic microorganisms. Symbiotic interactions can be neutral, harmful or have beneficial effects on the host organism. However, growing evidence suggests that microbial symbionts can evolve rapidly, resulting in drastic transitions along the parasite-mutualist continuum. In this Review, we integrate theoretical and empirical findings to discuss the mechanisms underpinning these evolutionary shifts, as well as the ecological drivers and why some host-microorganism interactions may be stuck at the end of the continuum. In addition to having biomedical consequences, understanding the dynamic life of microorganisms reveals how symbioses can shape an organism's biology and the entire community, particularly in a changing world.

Characterization of bacterial communities in wastewater with enhanced taxonomic resolution by full-length 16S rRNA sequencing

Wastewater treatment is crucial to environmental hygiene in urban environments. However, wastewater treatment plants (WWTPs) collect chemicals, organic matter, and microorganisms including pathogens and multi-resistant bacteria from various sources which may be potentially released into the environment via WWTP effluent. To better understand microbial dynamics in WWTPs, we characterized and compared the bacterial community of the inflow and effluent of a WWTP in Berlin, Germany using full-length 16S rRNA gene sequences, which allowed for species level determination in many cases and generally resolved bacterial taxa. Significantly distinct bacterial communities were identified in the wastewater inflow and effluent samples. Dominant operational taxonomic units (OTUs) varied both temporally and spatially. Disease associated bacterial groups were efficiently reduced in their relative abundance from the effluent by the WWTP treatment process, except for Legionella and Leptospira species which demonstrated an increase in relative proportion from inflow to effluent. This indicates that WWTPs, while effective against enteric bacteria, may enrich and release other potentially pathogenic bacteria into the environment. The taxonomic resolution of full-length 16S rRNA genes allows for improved characterization of potential pathogenic taxa and other harmful bacteria which is required to reliably assess health risk.

Comparative Transcriptomic Profiling of Yersinia enterocolitica O:3 and O:8 Reveals Major Expression Differences of Fitness- and Virulence-Relevant Genes Indicating Ecological Separation

Yersinia enterocolitica is a major diarrheal pathogen and is associated with a large range of gut-associated diseases. Members of this species have evolved into different phylogroups with genotypic variations. We performed the first characterization of the Y. enterocolitica transcriptional landscape and tracked the consequences of the genomic variations between two different pathogenic phylogroups by comparing their RNA repertoire, promoter usage, and expression profiles under four different virulence-relevant conditions. Our analysis revealed major differences in the transcriptional outputs of the closely related strains, pointing to an ecological separation in which one is more adapted to an environmental lifestyle and the other to a mostly mammal-associated lifestyle. Moreover, a variety of pathoadaptive alterations, including alterations in acid resistance genes, colonization factors, and toxins, were identified which affect virulence and host specificity. This illustrates that comparative transcriptomics is an excellent approach to discover differences in the functional output from closely related genomes affecting niche adaptation and virulence, which cannot be directly inferred from DNA sequences.

Yersinia enterocolitica is a zoonotic pathogen and an important cause of bacterial gastrointestinal infections in humans. Large-scale population genomic analyses revealed genetic and phenotypic diversity of this bacterial species, but little is known about the differences in the transcriptome organization, small RNA (sRNA) repertoire, and transcriptional output. Here, we present the first comparative high-resolution transcriptome analysis of Y. enterocolitica strains representing highly pathogenic phylogroup 2 (serotype O:8) and moderately pathogenic phylogroup 3 (serotype O:3) grown under four infection-relevant conditions. Our transcriptome sequencing (RNA-seq) approach revealed 1,299 and 1,076 transcriptional start sites and identified strain-specific sRNAs that could contribute to differential regulation among the phylogroups. Comparative transcriptomics further uncovered major gene expression differences, in particular, in the temperature-responsive regulon. Multiple virulence-relevant genes are differentially regulated between the two strains, supporting an ecological separation of phylogroups with certain niche-adapted properties. Strong upregulation of the ystA enterotoxin gene in combination with constitutive high expression of cell invasion factor InvA further showed that the toxicity of recent outbreak O:3 strains has increased. Overall, our report provides new insights into the specific transcriptome organization of phylogroups 2 and 3 and reveals gene expression differences contributing to the substantial phenotypic differences that exist between the lineages.

IMPORTANCEYersinia enterocolitica is a major diarrheal pathogen and is associated with a large range of gut-associated diseases. Members of this species have evolved into different phylogroups with genotypic variations. We performed the first characterization of the Y. enterocolitica transcriptional landscape and tracked the consequences of the genomic variations between two different pathogenic phylogroups by comparing their RNA repertoire, promoter usage, and expression profiles under four different virulence-relevant conditions. Our analysis revealed major differences in the transcriptional outputs of the closely related strains, pointing to an ecological separation in which one is more adapted to an environmental lifestyle and the other to a mostly mammal-associated lifestyle. Moreover, a variety of pathoadaptive alterations, including alterations in acid resistance genes, colonization factors, and toxins, were identified which affect virulence and host specificity. This illustrates that comparative transcriptomics is an excellent approach to discover differences in the functional output from closely related genomes affecting niche adaptation and virulence, which cannot be directly inferred from DNA sequences.

Phenotypic and genotypic presence of the Yersinia virulence plasmid do not affect the production of enterotoxin YstA by Yersinia enterocolitica strains

The aim of the study was to determine whether the presence of the Yersinia virulence plasmid could affect the production of enterotoxin YstA by Y. enterocolitica strains isolated from pigs which are the main source of infection for humans. The phenotypic features characteristic for the Yersinia virulence plasmid were detected on CRMOX agar in 8 out of 12 strains producing enterotoxin YstA, in 5 out of 12 doubtful strains, and in 11 out of 12 strains not producing YstA. Autoagglutination ability was detected in all 12 Y. enterocolitica strains that were positive in the suckling mice bioassay, in 11 doubtful strains and 10 negative strains. CRMOX+ colonies were generally ystA, myfA, virF and yadA positive, while CRMOX- colonies were only ystA and myfA positive. The amplicons of yadA were not detected in 2 (8.3%) out of 24 CRMOX+ and virF positive strains. The results of this study indicate that the presence of pYV does not affect the enterotoxin-producing ability of Y. enterocolitica strains.

The Most Important Virulence Markers of Yersinia enterocolitica and Their Role during Infection

Yersinia enterocolitica is the causative agent of yersiniosis, a zoonotic disease of growing epidemiological importance with significant consequences for public health. This pathogenic species has been intensively studied for many years. Six biotypes (1A, 1B, 2, 3, 4, 5) and more than 70 serotypes of Y. enterocolitica have been identified to date. The biotypes of Y. enterocolitica are divided according to their pathogenic properties: the non-pathogenic biotype 1A, weakly pathogenic biotypes 2⁻5, and the highly pathogenic biotype 1B. Due to the complex pathogenesis of yersiniosis, further research is needed to expand our knowledge of the molecular mechanisms involved in the infection process and the clinical course of the disease. Many factors, both plasmid and chromosomal, significantly influence these processes. The aim of this study was to present the most important virulence markers of Y. enterocolitica and their role during infection.

'Add, stir and reduce': Yersinia spp. as model bacteria for pathogen evolution

Pathogenic species in the Yersinia genus have historically been targets for research aimed at understanding how bacteria evolve into mammalian pathogens. The advent of large-scale population genomic studies has greatly accelerated the progress in this field, and Yersinia pestis, Yersinia pseudotuberculosis and Yersinia enterocolitica have once again acted as model organisms to help shape our understanding of the evolutionary processes involved in pathogenesis. In this Review, we highlight the gene gain, gene loss and genome rearrangement events that have been identified by genomic studies in pathogenic Yersinia species, and we discuss how these findings are changing our understanding of pathogen evolution. Finally, as these traits are also found in the genomes of other species in the Enterobacteriaceae, we suggest that they provide a blueprint for the evolution of enteropathogenic bacteria.

Thermal control of virulence factors in bacteria: a hot topic

Pathogenic bacteria sense environmental cues, including the local temperature, to control the production of key virulence factors. Thermal regulation can be achieved at the level of DNA, RNA or protein and although many virulence factors are subject to thermal regulation, the exact mechanisms of control are yet to be elucidated in many instances. Understanding how virulence factors are regulated by temperature presents a significant challenge, as gene expression and protein production are often influenced by complex regulatory networks involving multiple transcription factors in bacteria. Here we highlight some recent insights into thermal regulation of virulence in pathogenic bacteria. We focus on bacteria which cause disease in mammalian hosts, which are at a significantly higher temperature than the outside environment. We outline the mechanisms of thermal regulation and how understanding this fundamental aspect of the biology of bacteria has implications for pathogenesis and human health.

Yersinia enterocolitica Isolates from Wild Boars Hunted in Lower Saxony, Germany

Yersiniosis is strongly associated with the consumption of pork contaminated with enteropathogenic Yersinia enterocolitica, which is harbored by domestic pigs without showing clinical signs of disease. In contrast to data on Y. enterocolitica isolated from conventionally reared swine, investigations into the occurrence of Y. enterocolitica in wild boars in Germany are rare. The objectives of the study were to get knowledge about these bacteria and their occurrence in wild boars hunted in northern Germany by isolation of the bacteria from the tonsils, identification of the bioserotypes, determination of selected virulence factors, macrorestriction analysis, multilocus sequence typing (MLST), and testing of antimicrobial susceptibility. Altogether, tonsils from 17.1% of 111 tested wild boars were positive for Y. enterocolitica by culture methods. All but two isolates belonged to biotype (BT) 1A, with the majority of isolates bearing a ystB nucleotide sequence which was revealed to have 85% identity to internal regions of Y. enterocolitica heat-stable enterotoxin type B genes. The remaining Y. enterocolitica isolates were identified to be BT 1B and did not carry the virulence plasmid. However, two BT 1A isolates carried the ail gene. Macrorestriction analysis and results from MLST showed a high degree of genetic diversity of the isolates, although the region where the samples were taken was restricted to Lower Saxony, Germany, and wild boars were shot during one hunting season. In conclusion, most Y. enterocolitica isolates from wild boars investigated in this study belonged to biotype 1A. Enteropathogenic Y. enterocolitica bioserotypes 4/O:3 and 2/O:9, usually harbored by commercially raised pigs in Europe, could not be identified.

Clinical isolates of Yersinia enterocolitica biotype 1A represent two phylogenetic lineages with differing pathogenicity-related properties

Background

Y. enterocolitica biotype (BT) 1A strains are often isolated from human clinical samples but their contribution to disease has remained a controversial topic. Variation and the population structure among the clinical Y. enterocolitica BT 1A isolates have been poorly characterized. We used multi-locus sequence typing (MLST), 16S rRNA gene sequencing, PCR for ystA and ystB, lipopolysaccharide analysis, phage typing, human serum complement killing assay and analysis of the symptoms of the patients to characterize 298 clinical Y. enterocolitica BT 1A isolates in order to evaluate their relatedness and pathogenic potential.

Results

A subset of 71 BT 1A strains, selected based on their varying LPS patterns, were subjected to detailed genetic analyses. The MLST on seven house-keeping genes (adk, argA, aroA, glnA, gyrB, thrA, trpE) conducted on 43 of the strains discriminated them into 39 MLST-types. By Bayesian analysis of the population structure (BAPS) the strains clustered conclusively into two distinct lineages, i.e. Genetic groups 1 and 2. The strains of Genetic group 1 were more closely related (97% similarity) to the pathogenic bio/serotype 4/O:3 strains than Genetic group 2 strains (95% similarity). Further comparison of the 16S rRNA genes of the BT 1A strains indicated that altogether 17 of the 71 strains belong to Genetic group 2. On the 16S rRNA analysis, these 17 strains were only 98% similar to the previously identified subspecies of Y. enterocolitica. The strains of Genetic group 2 were uniform in their pathogenecity-related properties: they lacked the ystB gene, belonged to the same LPS subtype or were of rough type, were all resistant to the five tested yersiniophages, were largely resistant to serum complement and did not ferment fucose. The 54 strains in Genetic group 1 showed much more variation in these properties. The most commonly detected LPS types were similar to the LPS types of reference strains with serotypes O:6,30 and O:6,31 (37%), O:7,8 (19%) and O:5 (15%).

Conclusions

The results of the present study strengthen the assertion that strains classified as Y. enterocolitica BT 1A represent more than one subspecies. Especially the BT 1A strains in our Genetic group 2 commonly showed resistance to human serum complement killing, which may indicate pathogenic potential for these strains. However, their virulence mechanisms remain unknown.

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.

Detection, semiquantitative enumeration, and antimicrobial susceptibility of Yersinia enterocolitica in pork and chicken meats in Italy

Yersinia enterocolitica is recognized as an etiological agent of gastroenteritis, lymphadenitis, and chronic sequelae. During 2006 and 2007, 205 samples (125 pork and 80 chicken meats) were collected in Italy and tested for detection and most-probable-number (MPN) enumeration of Y. enterocolitica organisms. The microorganism was isolated from 45 samples (21.9%): 19 (15.2%) pork samples and 26 (32.5%) chicken samples. Y. enterocolitica MPN contamination levels were low, ranging from 0.30 to 1.50/g. Most (94.4%) Y. enterocolitica strains were biotype 1A (serotypes O:3; O:5; O:6,30; O:6,30-6,31; O:7,8-8-8,19; O:8; O:9; O:25,35; O:36; and O nontypeable), and 5.6% of the isolates were bioserotype 2/O:9. All isolates were tested for yadA, ail, inv, ystA, and ystB virulence sequences. The yadA gene was detected in two strains (3.7%) isolated from chicken samples: one Y. enterocolitica 2/O:9 yadA+ ail+ ystA+, and one Y. enterocolitica 1A/O:7,8-8-8,19 yadA+ inv+ ystB+. Two (3.7%) 2/O:9 strains, isolated from pork products, were ail+ ystA+. Most biotype 1A strains were ystB+ (84.3%) and inv+ (39.2%). All strains were sensitive to cefotaxime, ciprofloxacin, chloramphenicol, nalidixic acid, streptomycin, sulfonamide, tetracycline, trimethoprim, and trimethoprim-sulfamethoxazole. Resistance to gentamicin and aztreonam was observed in 1.9% of the isolates. High levels of resistance were detected toward amoxicillin-clavulanic acid (27.8%), ampicillin (75.9%), and erythromycin (100%). The authors hypothesize that Y. enterocolitica pathogenic biotypes are rather uncommon in foods when compared with their isolation rates from animal sources and that chicken meat could be contaminated as well as pig meat and its derived products.

Investigation of virulence genes in clinical isolates of Yersinia enterocolitica

In this study, we aimed to investigate the distribution of virulence genes in clinical isolates of pathogenic Yersinia enterocolitica. Two thousand six hundred stool samples were collected from 2600 patients with diarrhea, and were tested using the culture method and real-time PCR. Then, all isolates of pathogenic Y. enterocolitica cultured from the culture method were examined for virulence genes (inv, ail, ystA, ystB, ystC, yadA, virF) by PCR and for the presence of plasmid by four phenotypic tests. As a result, 160 pathogenic strains were successfully detected by the culture method, including bio/serotype 1A/unknown (4), 1B/unknown (8), 2/O:9 (39), 2/unknown (7), 3/O:3 (22), 3/unknown (6), 4/O:3 (55), 4/unknown (10) and 5/unknown (9). The positive rate of virulence genes tested in 160 isolates was inv (100%), ail (94%), ystA (93%), ystB (7.5%), ystC (5%), yadA (89%) and virF (82%) while the phenotypic test included autoagglutination (87%), binding of crystal violet (89%), calcium-dependent growth (74%) and Congo red absorption (78%), respectively. Finally, we found that not all pathogenic Y. enterocolitica necessarily carry all traditional virulence genes in both chromosomes and plasmids to cause illness. Perhaps, some of them, lacking some traditional virulence genes, contain other unknown virulence markers that interact with each other and play an important role in the diverse pathogenesis of pathogenic Y. enterocolitica.

YtxR, a conserved LysR-like regulator that induces expression of genes encoding a putative ADP-ribosyltransferase toxin homologue in Yersinia enterocolitica

Yersinia enterocolitica causes human gastroenteritis, and many isolates have been classified as either "American" or "non-American" strains based on their geographic prevalence and virulence properties. In this study we describe identification of a transcriptional regulator that controls expression of the Y. enterocolitica ytxAB genes. The ytxAB genes have the potential to encode an ADP-ribosylating toxin with similarity to pertussis toxin. However, a ytxAB null mutation did not affect virulence in mice. Nevertheless, the ytxAB genes are conserved in many Y. enterocolitica strains. Interestingly, American and non-American strains have different ytxAB alleles encoding proteins that are only 50 to 60% identical. To obtain further insight into the ytxAB locus, we investigated whether it is regulated as part of a known or novel regulon. Transposon mutagenesis identified a LysR-like regulator, which we designated YtxR. Expression of ytxR from a nonnative promoter increased Phi(ytxA-lacZ) operon fusion expression up to 35-fold. YtxR also activated expression of its own promoter. DNase I footprinting showed that a His(6)-YtxR fusion protein directly interacted with the ytxA and ytxR control regions at similar distances upstream of their probable transcription initiation sites, identified by primer extension. Deletion analysis demonstrated that removal of the regions protected by His(6)-YtxR in vitro eliminated YtxR-dependent induction in vivo. The ytxAB locus is not present in most Yersinia species. In contrast, ytxR is conserved in multiple Yersinia species, as well as in the closely related organisms Photorhabdus luminescens and Photorhabdus asymbiotica. These observations suggest that YtxR may play a conserved role involving regulation of other genes besides ytxAB.

Significance of heat-stable and heat-labile enterotoxins in porcine colibacillosis in an additive model for pathogenicity studies

Although heat-stable (ST) and heat-labile (LT) enterotoxins produced by enterotoxigenic Escherichia coli (ETEC) have been documented as important factors associated with diarrheal diseases, investigations assessing the contributions of individual enterotoxins to the pathogenesis of E. coli infection have been limited. To address the individual roles of enterotoxins in the diarrheal disease caused by K88-positive ETEC in young pigs, enterotoxin-positive and -negative isogenic E. coli strains were constructed by using pBR322 to clone and express LT and STb. Four strains, K88+ astA, K88+ astA/pBR322, K88+ astA STb+, and K88+ astA LT+, were constructed and subsequently included in gnotobiotic piglet challenge studies, and their pathogenesis was assessed. The results indicated that all K88+ isogenic strains were able to colonize the small intestines of piglets exhibiting the K88 receptor. However, only LT- and STb-positive strains caused appreciable diarrhea. Piglets inoculated with the K88+ astA LT+ strain became dehydrated within 18 h, while those inoculated with the K88+ astA STb+ strain did not, although diarrhea developed in several piglets. The changes in the blood packed-cell volume and plasma total protein of gnotobiotic piglets inoculated with the LT-positive strains were significantly greater than those of pigs inoculated with the K88 astA/pBR322 strain (P = 0.012, P = 0.002). Immunochemistry image analysis also suggested that LT enhanced bacterial colonization in a gnotobiotic piglet model. This investigation suggested that LT is a major contributor to the virulence of K88+ ETEC and that isogenic constructs are a useful tool for studying the pathogenesis of ETEC infection.

Inv-mediated apoptosis of epithelial cells infected with enteropathogenic Yersinia: A protective effect of lactoferrin

Yersinia spp., Gram-negative bacteria infecting animals and humans, contain plasmid and chromosomal genes coding for different virulence factors, of which outer membrane proteins are the most important. Among these, the inv gene product allows bacterial adherence and penetration of cells exposed at the intestinal lumen surface, and subsequent colonization of lymph nodes. In this research, we have studied the effects of bovine lactoferrin (bLf) on Y. enterocolitica and Y. pseudotuberculosis Inv-mediated interactions with epithelial cells. In particular, we analyzed bLf activity toward adhesion, invasion, and cell death induction by Yersinia spp. and the Escherichia coli HB101 (pRI203) strain (expressing the cloned Yersinia inv gene). Results showed that bLf was ineffective in bacterial adhesivity and invasivity whereas it inhibited apoptosis with a dose-dependent relationship. As epithelial cell apoptosis helps enteropathogenic Yersinia to attack the host and to gain access to the tissue, our results demonstrate a new potential antimicrobial application for bLf.

Comparison of the course of infection of virulent Yersinia enterocolitica serotype O:8 with an isogenic sodA mutant in the peroral rabbit model

Peroral infections of rabbits with a virulent Yersinia enterocolitica serotype O:8 wild-type strain (WA-314) and its isogenic Mn-cofactored superoxide dismutase (sodA) mutant were analyzed with respect to the following parameters: clinical findings, bacterial ability to colonize and persist in different tissues, bacterial resistance to the killing effect of leukocytes and blood sera, IgG antibody response, pathomorphological and immunomorphological changes. In comparison to WA-314, the sodA mutant was markedly impaired in its ability to disseminate into the brain and viscera, and to cause hyperthermia, leukocytosis with monocytosis, granulocytosis and initial lymphopenia. The sodA mutant strain was more susceptible to bactericidal activity of leukocytes and blood sera than the parent strain WA-314. Moreover, in comparison to WA-314, the sodA mutant was attenuated for mice after oral, intravenous, and intraperitoneal inoculation and totally avirulent for rats. Strikingly, the sodA mutation led not only to attenuation of virulence but also enhanced immunogenicity (as reflected by the specific antibody response). These features are consistent with the mild immunomorphological changes observed after infection with the sodA mutant as compared to the severe tissue lesions caused by the virulent strain WA-314. In conclusion, this study demonstrates that the sodA mutation in Y. enterocolitica leads to loss of virulence and gain of immunogenicity in rabbits. These are promising features for a live oral vaccine carrier strain.

Production of Yersinia stable toxin (YST) and distribution of yst genes in biotype 1A strains of Yersinia enterocolitica

Two hundred and fifty nine isolates of Yersinia enterocolitica and related species were examined for the production of heat-stable enterotoxin (Yersinia stable toxin; YST) as well as for the prevalence of enterotoxin genes, viz. ystA, ystB and ystC. Under the conventional conditions used for the production of Y. enterocolitica enterotoxin, i.e. in tryptic soy broth (TSB) supplemented with yeast extract at 28 °C for 48 h, 77.7 % of clinical isolates and 62.3 % of swine isolates showed enterotoxigenicity in infant mice. All isolates that produced enterotoxin at 28 °C also showed enterotoxic activity at 37 °C after 48 h incubation under an alkaline pH of 7.5, the pH present in the ileum. All Yersinia intermedia and Yersinia frederiksenii isolates were negative for enterotoxin production. All clinical isolates and 96.3 % of Y. enterocolitica isolates from swine hybridized with a probe for ystB, which indicated that the ystB gene was most prevalent in Y. enterocolitica biotype 1A strains. None of the Y. enterocolitica isolates showed hybridization with oligonucleotide probes for ystA or ystC. The study indicated that YST-b was the major contributor to diarrhoea produced by biotype 1A strains of Y. enterocolitica.

Effect of bovine lactoferricin on enteropathogenic Yersinia adhesion and invasion in HEp-2 cells

Bovine lactoferricin, a pepsin-generated antimicrobial peptide from bovine lactoferrin active against a wide range of bacteria, was tested for its ability to influence the adhesion and invasion of Yersinia enterocolitica and Yersinia pseudotuberculosis in HEp-2 cells. The addition of non-cytotoxic and non-bactericidal concentrations of lactoferricin to cell monolayers before infection, under different bacterial growth experimental conditions, was ineffective or resulted in about a 10-fold increase in bacterial adhesion, whereas, in bacteria grown in conditions allowing maximal inv gene expression, a 10-fold inhibition of cell invasion by lactoferricin was observed. To confirm that the anti-invasive activity of lactoferricin was exerted against invasin-mediated bacterial entry, experiments were also performed utilizing Escherichia coli strain HB101 (pRI203), harbouring the inv gene from Y. pseudotuberculosis, which allows penetration of mammalian cells. Under these experimental conditions, lactoferricin was able to inhibit bacterial entry into epithelial cells, demonstrating that this peptide acts on inv-mediated Yersinia species invasion. As the inv gene product is the most important virulence factor in enteropathogenic Yersinia, being responsible for bacterial adherence and penetration within epithelial cells of the intestinal lumen and for the subsequent colonization of regional lymph nodes, these data provide additional information on the protective role of lactoferricin against bacterial infection.

Virulence characteristics and epidemiology of Yersinia enterocolitica and Yersiniae other than Y. pseudotuberculosis and Y. pestis isolated from water and sewage

AIMS

To determine the species, bio-sero-phagetypes, antimicrobial drug resistance and also the pathogenic potential of 144 strains of Yersinia spp. isolated from water sources and sewage in Brazil.

METHODS AND RESULTS

The 144 Yersinia strains were characterized biochemically, serologically and had their antibiotic resistance and phenotypic virulence markers determined by microbiological and serological standard techniques. The Y. enterocolitica strains related to human diseases were also tested for the presence of virulence genes, by the PCR technique. The isolates were classified as Y. enterocolitica, Y. intermedia, Y. frederiksenii, Y. kristensenii and Yersinia biochemically atypical. The 144 isolates belonged to various bio-serogroups. Half of the strains showed resistance to three or more drugs. The Y. enterocolitica strains related to human diseases exhibited phenotypic virulence characteristics and virulence genes.

CONCLUSIONS

Water from various sources and sewage are contaminated with Yersinia spp. in Brasil. Among these bacteria, virulent strains of Y. enterocolitica were found, with biotypes and serogroups related to human diseases.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first documented description of the occurrence of pathogenic Y. enterocolitica in water sources and sewage in Brazil. The occurrence of virulence strains of Y. enterocolitica shows that the environment is a potential source of human infection by this species in this country.

The yersiniae--a model genus to study the rapid evolution of bacterial pathogens

Yersinia pestis, the causative agent of plague, seems to have evolved from a gastrointestinal pathogen, Yersinia pseudotuberculosis, in just 1,500-20,000 years--an 'eye blink' in evolutionary time. The third pathogenic Yersinia, Yersinia enterocolitica, also causes gastroenteritis but is distantly related to Y. pestis and Y. pseudotuberculosis. Why do the two closely related species cause remarkably different diseases, whereas the distantly related enteropathogens cause similar symptoms? The recent availability of whole-genome sequences and information on the biology of the pathogenic yersiniae have shed light on this paradox, and revealed ways in which new, highly virulent pathogens can evolve.

Pathogenicity of Yersinia enterocolitica biotype 1A

Yersinia enterocolitica strains of biotype 1A lack the known virulence determinants of strains in other categories, including the Yersinia virulence plasmid (pYV), and several chromosomal markers of pathogenicity. For this reason, and also because Y. enterocolitica strains of biotype 1A are frequently isolated from the environment or asymptomatic individuals, these bacteria are often assumed to be avirulent. On the other hand, there is a considerable body of clinical, epidemiological and experimental evidence to indicate that at least some strains of Y. enterocolitica biotype 1A are able to cause gastrointestinal symptoms which resemble those caused by pYV-bearing strains. The availability of a number of experimental systems, including cell culture and animal models of infection, provides an opportunity to identify and characterise the essential virulence determinants of biotype 1A strains.

Experimental mixed infection of rabbits with Yersinia enterocolitica and Listeria monocytogenes

Experimental mixed infection was reproduced in rabbits after per os infection with Yersinia enterocolitica serotype 0:3 cells. Four days later some of animals were re-infected orally with Listeria monocytogenes serotype 4b cells. A third group of healthy rabbits was also infected per os with Listeria monocytogenes. The infectious process was followed dynamically from days 1-28. The experimental animals were examined for clinical, paraclinical and morphological findings. Augmentation of body temperature and alveolar macrophage number, a decreased number of peritoneal macrophages, leucopenia as well as purulent meningoencephalitis, catarrhal pneumonia, lienitis, lymphadenitis and enteritis were detected after experimental mixed infection. Both types of macrophages demonstrated a weak bactericidal activity against Yersinia enterocolitica and a highly expressed killing effect against Listeria monocytogenes. Yersinia and Listeria cells were isolated from the viscera and brain. Both species of bacteria were established intracellularly in the macrophages by electron-microscopic examination. The data received showed that mixed Yersinia enterocolitica 0:3 and Listeria monocytogenes 4b infection of rabbits runs with transitory hyperthermia as a generalized infection and is similar to the Listeria mono-infection. The immunosuppressive effect induced by oral Yersinia enterocolitica infection of rabbits promotes the expression of listerious agents.

Yersinia virulence: more than a plasmid

The genus Yersinia is composed of 11 species, three of which are pathogenic in humans. The three pathogens, Y. pestis, Y. enterocolitica, and Y. pseudotuberculosis, cause a broad spectrum of disease ranging from pneumonic plague to acute gastroenteritis. Each of the three requires a large, well-defined plasmid for full virulence, as well as many chromosomally encoded virulence factors (CEVF). This review will describe these CEVF and their roles in virulence. In addition, a possible model for key events in Y. enterocolitica pathogenesis is described based on information revealed by analysis of several of the CEVF.

Arthritis after experimental infection with Yersinia enterocolitica 0:3 in rabbits

Arthritis in rabbits was caused after experimental oral infection with Yersinia enterocolitica (serotype 0:3, biotype 4, pYV+). Clinical and laboratory signs, bacterial dissemination to the viscera, immune response and morphological findings were studied from day 1 to day 40 post-infection (p.i.). Augmentation of body temperature and erythrocyte sedimentation rate occurred on day 1, and on day 8 p.i. was accompanied by leucopenia. The number of alveolar macrophages was increased up to the 15th day p.i., in contrast to peritoneal macrophage numbers. Extensive bacterial colonization of the internal organs was detected at necropsy until the end of the experiment. Analysis of the cell immune response revealed activation of B cells in peripheral blood, spleen and thymus as well as augmentation of T-cell number in the lymphoid organs examined on days 15, 28 and 40 p.i. Histological changes typical of a generalized infection, such as purulent meningoencephalitis, catarrhal pneumonia and lymphadenitis, were observed. Clinical and morphological manifestations of arthritis were also established. The results obtained show that Y. enterocolitica (serotype 0:3, pYV+) induces a generalized, non-lethal infection in Chinchilla rabbits, complicated by arthritis.

Dendritic cell function is perturbed by Yersinia enterocolitica infection in vitro

Infection with Yersinia enterocolitica is the cause of intestinal or extraintestinal diseases. We investigated the role of dendritic cells (DC), the most potent antigen-presenting cell (APC), in the course of infection with Y. enterocolitica in vitro. For these studies, DC were isolated from human peripheral blood and infected with green fluorescent protein (GFP)-labelled Y. enterocolitica. Bacteria were found within DC by FACS analysis and viable bacteria could be cultured from lysed cells. Within 24 h after infection, DC upregulated CD83 and CD86 followed at day 3, indicating maturation of DC. In contrast, for MHC class II, a marked but transient downregulation was observed at day 3 after infection, and downregulation to a lesser extent for CD80 at day 5. To assess the immunostimulatory capacity of DC, viable infected and uninfected DC were incubated with autologous T cells in the presence of phytohemagglutinin A (PHA). T cell proliferation was significantly reduced at days 4-6 after infection but not thereafter, whereas nonpathogenic Escherichia coli was not able to mimick this suppressive effect of Y. enterocolitica. The same suppression could be observed when infected DC were used in a mixed leucocyte reaction with allogeneic T cells. Thus Y. enterocolitica is able to invade DC, does not induce necrosis or apoptosis, but affects maturation of DC. However, MHC class II-molecules are downregulated initially, which coincides with a diminished immunostimulatory capacity of DC infected with Y. enterocolitica. The diminished immunostimulatory capacity of DC following infection with Y. enterocolitica in vitro might impair or delay elimination of bacteria thereby contributing to pathogenesis of bacterial enteritis or extraintestinal manifestations such as reactive arthritis.

Yersinia enterocolitica biogroup 1A, serotype O:5 in chicken carcasses

To evaluate the presence of Yersinia enterocolitica in raw chicken, 70 samples of chicken carcasses were obtained from a Buenos Aires, Argentina, processing plant. The detection of this psychotropic microorganism was carried out using the whole carcass rinse method and enrichment in phosphate-buffered saline, 0.067 M, pH 7.6, at 4 degrees C, followed by alkaline treatment and isolation on cefsulodin-irgasan-novobiocin nutrient agar. Y. enterocolitica or related species were detected in 7 of 70 samples. From them, 4.3% were identified as Y. enterocolitica, 1.4% as Yersinia intermedia, and 4.3% as Yersinia frederiksenii. The serotype and phagotype of Y. intermedia isolates were O:5(2), 5(3), and Xz and those of Y. frederiksenii were O:4.16 and Xo. All Y. enterocolitica isolates belong to the biogroup 1A, serotype O:5, phagotype Xz, which presents uncertain pathogenic potential. These findings reinforce the worldwide concern on the microbiological quality of food products. Quality assurance programs on the whole poultry process are increasingly being adopted in Argentina.

Yersinia enterocolitica invasin protein triggers differential production of interleukin-1, interleukin-8, monocyte chemoattractant protein 1, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor alpha in epithelial cells: implications for understanding the early cytokine network in Yersinia infections

Yersinia enterocolitica infection of epithelial cells results in interleukin-8 (IL-8) mRNA expression. Herein we demonstrate that besides IL-8, increased mRNA levels of five other cytokines, IL-1alpha, IL-1beta, monocyte chemoattractant protein 1 (MCP-1), granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor alpha (TNF-alpha), can be detected upon infection of HeLa cells with Yersinia. Yersinia-triggered cytokine production was not affected by blocking phosphatidylinositol-3-phosphate kinase with wortmannin, which inhibited bacterial invasion. Comparable cytokine mRNA responses were triggered by Escherichia coli expressing Yersinia inv, while no response was triggered by an inv-deficient Yersinia mutant. Moreover, cytokine responses were independent from metabolic activity of the bacteria, as killed bacterial cells were sufficient for triggering cytokine responses in HeLa cells. Semiquantitative reverse transcription-PCR analysis was used to assess the kinetics of cytokine mRNA expression in infected HeLa cells. IL-8, IL-1alpha, IL-1beta, MCP-1, GM-CSF, and TNF-alpha mRNA expression increased within 1 h postinfection, reached a maximum after 3 to 4 h, and then declined to preinfection levels within 3 h. IL-8, MCP-1, and GM-CSF were secreted by HeLa cells, whereas IL-1alpha and IL-1beta were not secreted and thus were found exclusively intracellularly. TNF-alpha protein could not be detected in cell lysates or supernatants. Stimulation of HeLa cells with IL-1alpha was followed by increased IL-8 mRNA expression, whereas stimulation with IL-8 did not induce cytokine production. Likewise, MCP-1 and GM-CSF did not induce significant cytokine responses in HeLa cells. Our results implicate that the initial host response to Yersinia infection might be sustained by IL-8, MCP-1, and GM-CSF produced by epithelial cells.

Yersiniae other than Y. enterocolitica, Y. pseudotuberculosis, and Y. pestis: the ignored species

The genus Yersinia is composed of 11 species, of which three (Y. pestis, Y. pseudotuberculosis, and Y. enterocolitica) have been exhaustively characterized. The remaining eight species (Y. frederiksenii, Y. intermedia, Y. kristensenii, Y. bercovieri, Y. mollaretii, Y. rohdei, Y. ruckeri, and Y. aldovae) have not been studied extensively and, because of the absence of classical Yersinia virulence markers, are generally considered to be nonpathogenic. However, recent data suggest that some of these eight species may cause disease by virtue of their having virulence factors distinct from those of Y. enterocolitica. These data raise intriguing questions about the mechanisms by which these species interact with their host cells and elicit human disease.

The Yersinia enterocolitica phospholipase gene yplA is part of the flagellar regulon

Yersinia enterocolitica yplA encodes a phospholipase required for virulence. Virulence genes are often regulated in response to environmental signals; therefore, yplA expression was examined using a yplA::lacZY transcriptional fusion. Maximal yplA expression occurred between pH 6.5 and pH 7.5 and was induced in the mid-logarithmic growth phase. Potential Fnr, cyclic AMP (cAMP)-cAMP receptor protein (Crp), and sigma(F) regulatory sites were identified in the nucleotide sequence. Reduction of yplA expression by aeration, addition of glucose and sucrose, and application of high temperature and salt is consistent with Fnr-, cAMP-Crp-, and sigma(F)-mediated regulation, respectively. Expression of yplA was reduced in flhDC and fliA null strains, indicating that yplA is part of the flagellar regulon.

Prevalence of yersinia plasmid-encoded outer protein (Yop) class-specific antibodies in multitransfused Greek patients with thalassemic syndromes

OBJECTIVE: To evaluate the prevalence of class-specific antibodies (G, A, M) to Yersinia enterocolitica plasmid-encoded outer proteins (Yops), in a closely followed multitransfused population of patients with thalassemia. METHODS: Sera from 408 beta-thalassemic patients and 386 healthy blood donors used as controls were analyzed with the enzyme-linked immunosorbent assay (ELISA) for IgG, IgA and IgM antibodies to yersinia outer proteins. The Yop antigen for the ELISA was prepared using a plasmid-bearing wild-type strain of Y. enterocolitica of serotype O:8. RESULTS: Anti-Yop IgG antibodies were detected in 84 out of 408 beta-thalassemic patients (20.6%) compared with only eight out of 386 (2.1%) healthy blood donors. None of the sera of either group was positive for anti-Yop IgA or IgM antibodies. On evaluating patients with registered clinical and laboratory signs of a previous yersinia infection in the period from 1978 to 1996, we found that those with a positive agglutination test for Y. enterocolitica infection at the time of manifestation showed a higher rate of persisting IgG seropositivity to Yops than those with positive culture and clinical signs only. A significant percentage (9.49%) of the seropositive patients had no registered data of a past Y. enterocolitica infection. There was remarkable persistence of anti-Yop IgG antibodies in the thalassemic population, even in patients infected during the early years of our study period (1978--80). CONCLUSIONS: The results suggest that the determination of class-specific antibodies to Yops, which are specific antigens for the pathogenic yersiniae (Y. enterocolitica, Y. pseudotuberculosis and Y. pestis), in addition to its usefulness in the diagnosis of infection, will be a very sensitive and specific index for epidemiologic studies.

Identification of virulence-associated characteristics in clinical isolates of Yersinia enterocolitica lacking classical virulence markers

Yersinia enterocolitica is an important enteric pathogen which has well-defined virulence determinants that allow the bacteria to become established in their hosts and overcome host defenses. A number of strains obtained from patients with diarrhea, however, lack these genes. Accordingly, the mechanisms by which they cause disease are uncertain. Most of these isolates belong to biotype 1A. Strains of this biotype are also frequently isolated from a variety of nonclinical sources, such as food, soil, water, and healthy animals, and there is evidence that some of these strains are avirulent. In this study we investigated 111 strains of Y. enterocolitica biotype 1A, 79 from symptomatic humans and 32 from nonclinical sources, for virulence-associated characteristics. DNA hybridization studies showed that none of the strains carried sequences homologous with pYV, the approximately 70-kb Yersinia virulence plasmid. Some strains hybridized with DNA probes for one of the following chromosomal virulence-associated genes: ail (7.2%), myfA (11.7%), ystA (0.9%), and ystB (85%). In addition, 33 strains (29.7%) produced an enterotoxin that was reactive in infant mice. However, the frequencies of these virulence-associated properties in clinical and nonclinical isolates were similar. Clinical isolates invaded HEp-2 cells and Chinese hamster ovary cells to a significantly greater extent than nonclinical strains (P < or = 0.002). In addition, clinical strains colonized the intestinal tracts of perorally inoculated mice for significantly longer periods than nonclinical isolates (P < or = 0.01). Light and electron microscopic examination of tissue culture cells incubated with invasive yersiniae revealed that the bacteria invaded selected cells in large numbers but spared others, suggesting that biotype-1A strains of Y. enterocolitica may invade cells by a novel mechanism. These results indicate that some clinical isolates of Y. enterocolitica which lack classical virulence markers may be able to cause disease via virulence mechanisms which differ from those previously characterized in enteropathogenic Yersinia species.

The novel heat-stable enterotoxin subtype gene (ystB) of Yersinia enterocolitica: nucleotide sequence and distribution of the yst genes

The gene (ystB) encoding the novel subtype of the heat-stable enterotoxin (Y-STb) was cloned from the chromosome of a clinical isolate of Yersinia enterocolitica 84-50 (serotype O:5, biotype 1A) and the nucleotide sequence was determined. The ystB contained 216 base pairs that encoded a protein of 71 amino acid residues. The C-terminal 30 residues of the precursor protein exactly corresponded to the amino acid sequence of the Y-STb toxin, purified from the culture supernatant of the wild strain. Homology search revealed that there are 76.9% nucleotide sequence similarity between ystB and the Yersinia kristensenii ST gene, and 73.5% with the Y. enterocolitica prototype sequence of yst (ystA). When tested with the PCR generated ystB specific probe, 36 of 304 Y. enterocolitica strains from 18 countries hybridized with the probe. All the ystB probe positive strains belonged to biotype 1A and mostly to the so-called non-pathogenic serotype O:5, O:6, O:7,8 O:7,13 and O:10, while ystA was predominantly found among the pathogenic serotypes (78.5%). Out of 36 ystB gene positive strains, 18 were clinical origin from six countries, which were also positive in the suckling mice assay suggesting that ystB may play an important role in the pathogenesis, and the so-called non-pathogenic serotypes could be virulent for human.

Yersinia enterocolitica: the charisma continues

Yersinia enterocolitica, a gram-negative coccobacillus, comprises a heterogeneous group of bacterial strains recovered from animal and environmental reservoirs. The majority of human pathogenic strains are found among distinct serogroups (e.g. O:3, O:5,27, O:8, O:9) and contain both chromosome- and plasmid (60 to 75 kb)-mediated virulence factors that are absent in "avirulent" strains. While Y. enterocolitica is primarily a gastrointestinal tract pathogen, it may produce extraintestinal infections in hosts with underlying predisposing factors. Postinfection sequelae include arthritis and erythema nodosum, which are seen mainly in Europe among patients with serogroups O:3 and O:9 infection and HLA-B27 antigen. Y. enterocolitica is acquired through the oral route and is epidemiologically linked to porcine sources. Bacteremia is prominent in the setting of immunosuppression or in patients with iron overload or those being treated with desferrioxamine. metastatic foci following bacteremia are common and often involve the liver and spleen. Of particular concern is blood transfusion-related bacteremia. Evidence has accumulated substantiating the role of Y. enterocolitica as a food-borne pathogen that has caused six major outbreaks in the United States. The diagnosis of Y. enterocolitica gastroenteritis is best achieved through isolation of the bacterium on routine or selective bacteriologic media. When necessary, serogrouping, biogrouping, and assessment for plasmid-encoded virulence traits may aid in distinguishing virulent from "avirulent" strains. Epidemiologically, outside of identified food-borne outbreaks, the source (reservoir) of Y. enterocolitica in sporadic cases is speculative. Therefore, prevention and control measures are difficult to institute.

Detection of pathogenic Yersinia enterocolitica using the multiplex polymerase chain reaction

A multiplex polymerase chain reaction (PCR) was developed to detect the presence of the ail, yst, and virF genes of Yersinia enterocolitica simultaneously, quickly and accurately. The amplified fragment sizes were 356 base-pairs (bp) for the ail gene, 134 bp for the yst gene, and 231 bp for the virF gene. The specificity of the amplified products was confirmed by hybridization with digoxigenin-labelled oligonucleotide probes. Amplification was successful whether the template was derived from a single colony of bacteria, aliquots of boiled bacterial suspensions, from DNA extracted from pure or mixed cultures or from stool specimens. Amplification of the virF gene was also achieved from strains of Y. pseudotuberculosis carrying the 70 kb plasmid but not with preparations from other related Yersinia species or from other members of the family Enterobacteriaceae. The detection limit we established was 5-10 colony forming units per millilitre (cfu/ml) and 1.0 pg of DNA.

Differential secretion of interleukin-8 by human epithelial cell lines upon entry of virulent or nonvirulent Yersinia enterocolitica

Epithelial cells of the intestinal mucosa are among the first cells encountered by invasive pathogens. Bacterial invasion of the mucosa gives rise to an inflammatory response, characterized by the influx of polymorphonuclear leukocytes. The chemotactic stimulus responsible for this accumulation is unknown, but several in vitro studies have demonstrated that epithelial cells secrete the chemokine interleukin-8 (IL-8), a potent chemoattractant of polymorphonuclear leukocytes, upon bacterial entry. In this study we analyzed the secretion of IL-8 by human intestinal (T84) and cervical (HeLa) epithelial cell lines in response to infection with the enteric pathogen Yersinia enterocolitica. IL-8 was secreted by T84 and HeLa cells in response to invasion by Y. enterocolitica. Virulent Y. enterocolitica induced a significantly lower level of IL-8 secretion than nonvirulent Y. enterocolitica. Subsequent analysis employing a mutant defective in Yop secretion and various yop mutants showed that the reduced secretion of IL-8 is due to the presence of Yop proteins. Our data suggest that YopB and YopD are required for the suppressive effect.

Association between clinical presentation, biogroups and virulence attributes of Yersinia enterocolitica strains in human diarrhoeal disease

Traditionally the enteric pathogen Yersinia enterocolitica has been differentiated into biogroups. Despite being considered as non-pathogenic, biogroup 1A isolates have constituted a sizeable fraction of strains from patients with gastroenteritis in many reports. To establish a potential clinical significance for biogroup 1A isolates of Y. enterocolitica, clinical disease in patients with gastroenteritis excreting such isolates was compared with symptoms among patients found infected with pathogenic biogroups. Clinical data and isolates of 66 patients from whom Y. enterocolitica had been isolated by direct plating were available for study. There was an association between patient age below 3 years and infection with 'pathogenic' Y. enterocolitica. The severity of gastroenteritis and other symptoms, however, did not depend on the biogroup, or the presence of the virulence plasmid in the yersinia strain isolated from the patients. Strains belonging to biogroup 1A of Y. enterocolitica showed two clusters of ribotypes, one of which encompassed most isolates recovered from humans, the other being associated with environmental isolates. This might indicate the existence of human-adapted and potentially pathogenic strains among biogroup 1A of Y. enterocolitica.

Environmental modulation of gene expression and pathogenesis in Yersinia

The yersiniae are a useful model for understanding how environmental modulation of gene expression allows pathogens to inhabit a wide range of niches. This review follows the enteropathogenic yersiniae, Yersinia enterocolitica and Yersinia pseudotuberculosis, and the agent of plague, Yersinia pestis, through their life cycles, describing how adaptive gene expression may promote successful pathogenesis.

In vitro and in vivo characterization of an ail mutant of Yersinia enterocolitica

Ail is a 17-kDa protein of Yersinia enterocolitica previously identified on the basis of its ability to confer upon Escherichia coli the phenotype of attachment and invasion of cultured epithelial cells. Here we report an examination of the contribution of ail to the pathogenicity of Y. enterocolitica. A low-copy-number ail plasmid that promoted serum resistance in E. coli HB101 was constructed. The serum resistance phenotype conferred by ail to E. coli was affected by the growth phase of the culture as well as by the gene copy number. In contrast, the copy number of ail (and the relative quantity of Ail) was found to have little effect on the amount of Ail-promoted invasion of cultured epithelial cells. An ail mutant of Y. enterocolitica was constructed and characterized in vitro. This mutant produced no detectable Ail and had a reduced ability to invade CHO cells. Serum resistance of Y. enterocolitica was Ail dependent and was affected by growth phase and ail copy number. The phenotype of the ail mutant was examined in vivo by using a murine model for infection. The ail mutant phenotype was identical to that of the wild-type strain in oral 50% lethal dose studies and early colonization of Peyer's patches as well as in kinetic studies. Western blot (immunoblot) analysis of Ail produced by bacteria growing in vivo at 48 h postinfection indicated that ail was expressed at this time point. Thus, our findings confirm that Ail contributes to the serum resistance and invasion phenotypes of Y. enterocolitica in vitro and indicate that Ail is not required to establish an infection or to cause systemic infection of BALB/c or DBA/2 mice.

The rpoS gene from Yersinia enterocolitica and its influence on expression of virulence factors

The chromosome of Yersinia enterocolitica encodes a heat-stable enterotoxin called Yst and a surface antigen called Myf, which closely resembles enterotoxin-associated fimbriae. Both factors could act in conjunction to produce diarrhea. Production of the enterotoxin is regulated by temperature, osmolarity, and pH and occurs only when bacteria reach the stationary phase. Myf production is regulated by temperature and pH and, as we show in this work, also occurs after the exponential growth phase. In an attempt to understand the late-phase expression of yst and myf, we cloned, sequenced, and mutagenized the gene encoding RpoS, an alternative sigma factor of the RNA polymerase involved in expression of stationary-phase genes in other enterobacteria. An intact rpoS gene was necessary for full expression of yst in the stationary phase but not for the expression of myf and of pYV-encoded virulence determinants.

Characterization of a highly toxic, large molecular size heat-stable enterotoxin produced by a clinical isolate of Yersinia enterocolitica

A novel heat-stable enterotoxin (ST) designated as Y-STc was purified to homogeneity from the culture supernatant of a pathogenic strain of Yersinia enterocolitica serotype O3 and its amino acid sequence was determined. The mature Y-STc was found to consist of 53 amino acid residues, which includes the putative pro-sequence. The molecular weight of Y-STc was 5638 and constituted the largest molecular size in the family of currently known STs. The minimum effective dose of purified Y-STc in the suckling mouse assay was 0.6 ng (0.0 pmol), indicating that, despite the long sequence, Y-STc is the most toxic in the ST family.

MyfF, an element of the network regulating the synthesis of fibrillae in Yersinia enterocolitica

The Yersinia enterocolitica surface antigen Myf is a fibrillar structure that resembles CS3 fimbriae. Gene myfA encodes the 21-kDa major subunit of the antigen, while genes myfB and myfC are required for the transport and assembly of pilin subunits at the bacterial cell surface. Here we show that the expression of Myf is regulated at the transcriptional level by temperature and pH. Gene myfA is transcribed at 37 degrees C and in acidic medium. The transcription start is preceded by a putative -10 box for the vegetative RNA polymerase as well as by sequences resembling the consensus sequence recognized by sigma 28. Thus, myfA could be transcribed either from a classical sigma 70 promoter or from a sigma 28 promoter. Transcription of myfA requires at least two genes, myfF and myfE, situated immediately upstream from myfA. The myfF product does not show similarity to any known regulatory protein. It is an 18.5-kDa protein with no typical helix-turn-helix motif and a unique hydrophobic domain in the NH2-terminal part. T7 expression, osmotic shock, fractionation experiments, and TnphoA fusion analyses carried out in Escherichia coli suggest that MyfF is associated with the inner membrane by means of its hydrophobic domain whereas the hydrophilic part protrudes in the periplasm. These features strikingly evoke ToxS, a protein involved in regulation of Tcp pilus production in Vibrio cholerae. MyfE resembles PsaE, a protein involved in regulation of pH6 antigen in Yersinia pestis. Genes myfF and myfE are presumably part of a whole regulatory network. MyfF could be an element of the signal transducing system.

Regulation of the Yersinia enterocolitica enterotoxin Yst gene. Influence of growth phase, temperature, osmolarity, pH and bacterial host factors

The chromosome of Yersinia enterocolitica encodes an enterotoxin called Yst. We analysed transcription of chromosomal yst'--luxAB and plasmid-borne yst'--lacZ operon fusions and we observed that regulation of yst expression occurs at transcriptional level. In a wild-type strain, yst was transcribed from at least two major promoters. yst transcription reached a maximum at the entry to the stationary phase and significantly varied in different Y. enterocolitica strains. In some strains, it gradually decreased during the course of our work, suggesting the existence of a mechanism switching the expression of yst to a silent state. Changes in the status of bacterial host factors rather than modifications in the yst gene are responsible for this silencing. Negative regulator YmoA participates in yst silencing and temperature regulation of yst. YmoA was also required for proper growth-phase regulation of yst, although it is not the only factor involved in this regulation. Physico-chemical parameters of the environment play an important role in yst transcription. In usual culture media (e.g. tryptic soy broth), the enterotoxin gene was transcribed only at temperatures below 30 degrees C, which argued against the role of Yst in a prolonged diarrhoea at body temperatures. However, yst transcription could be induced at 37 degrees C by increasing osmolarity and pH to the values normally present in the ileum lumen. This finding reconciles the observations concerning yst expression in a host environment and in bacterial cultures, thus supporting the idea that enterotoxin Yst is a virulence factor of Y. enterocolitica.

Role of YadA in arthritogenicity of Yersinia enterocolitica serotype O:8: experimental studies with rats

Outer membrane protein YadA, the Yersinia adhesin, is one of the plasmid-encoded virulence factors of yersiniae. To evaluate the role of YadA in the pathogenesis of reactive arthritis experimentally, we used YadA- strain YeO8-116, a kanamycin GenBlock insertion mutant derived from Yersinia enterocolitica O:8 wild-type strain 8081. As control strains, a plasmid-cured derivative (8081-c) of 8081 and a YopH- mutant (8081-yoph) were used. In addition, YeO8-116, with the yadA mutation transcomplemented with plasmid pMW10, was used. YeO8-116 induced arthritis to a considerably lesser extent than did wild-type strain 8081 when inoculated intravenously into Lewis rats. In rats surviving for over 14 days after the bacterial inoculation, the arthritis incidences were 6% (4 of 72) among those inoculated with the yadA mutant and 51% (33 of 65) among those inoculated with wild-type strain 8081. When the yadA gene was transcomplemented back to YeO8-116, YeO8-116/pMW10 induced arthritis in 47% (9 of 19) of the inoculated rats. Plasmid-cured strain 8081-c did not induce arthritis in any of the 24 inoculated rats, whereas YopH- mutant 8081-yoph induced arthritis in 20% (5 of 25) of the rats inoculated. Although the 50% lethal dose of YeO8-116 was about sixfold higher than that of 8081, the kinetics of bacterial elimination from the spleen and mesenteric lymph nodes were about the same with both strains. Antibody responses in rats infected with the two strains were also indistinguishable. Our results indicate that YadA contributes to the arthritogenicity of Y. enterocolitica in the rat model.