Yersinia pseudotuberculosis Exploits CD209 Receptors for Promoting Host Dissemination and Infection.

Yersinia pseudotuberculosis is a Gram-negative enteropathogen and causes gastrointestinal infections. It disseminates from gut to mesenteric lymph nodes (MLNs), spleen, and liver of infected humans and animals. Although the molecular mechanisms for dissemination and infection are unclear, many Gram-negative enteropathogens presumably invade the small intestine via Peyer's patches to initiate dissemination. In this study, we demonstrate that Y. pseudotuberculosis utilizes its lipopolysaccharide (LPS) core to interact with CD209 receptors, leading to invasion of human dendritic cells (DCs) and murine macrophages. These Y. pseudotuberculosis-CD209 interactions result in bacterial dissemination to MLNs, spleens, and livers of both wild-type and Peyer's patch-deficient mice. The blocking of the Y. pseudotuberculosis-CD209 interactions by expression of O-antigen and with oligosaccharides reduces infectivity. Based on the well-documented studies in which HIV-CD209 interaction leads to viral dissemination, we therefore propose an infection route for Y. pseudotuberculosis where this pathogen, after penetrating the intestinal mucosal membrane, hijacks the Y. pseudotuberculosis-CD209 interaction antigen-presenting cells to reach their target destinations, MLNs, spleens, and livers.

Modulation of posterior intestinal mucosal proteome in rainbow trout (Oncorhynchus mykiss) after Yersinia ruckeri infection.

Yersinia ruckeri is the causative agent of enteric redmouth disease in salmonids. In fish, the intestine represents an important site of nutrient uptake, host-pathogen interactions, and defense. The posterior intestine can be inflamed, reddened, and filled with an opaque, yellowish fluid during Y. ruckeri infection. Herein, we report an investigation on the proteome alteration in the posterior intestinal mucosa of rainbow trout (Oncorhynchus mykiss) after exposure to Y. ruckeri. The intestinal mucosal proteins were identified and quantified by a shotgun proteomic approach by applying data-independent quantification with sequential windowed acquisition of all theoretical mass spectra (SWATH). A total of 437 proteins were found to be differentially up- or downregulated in the posterior intestine. Gene ontology of upregulated proteins pointed to their involvement into exopeptidase, endopeptidase, and hydrolase activities, while the downregulated proteins were involved in lipid metabolism, actin binding, and translation processes. Additionally, upregulated proteins were predicted to be involved in lysosome, oxidative phosphorylation, and metabolic pathways, while downregulated proteins were implicated in focal adhesion, regulation of actin cytoskeleton, protein digestion and absorption pathways. This study showed that Y. ruckeri infection can alter protein abundance involved in serine-type carboxypeptidase, cysteine and aspartic-type endopeptidases, metallopeptidases, antioxidant defense, calcium ion binding, glycolytic and carbohydrate metabolic processes in the proteome of the intestinal mucosa of rainbow trout.

Experimental infection by Yersinia ruckeri O1 biotype 2 induces brain lesions and neurological signs in rainbow trout (Oncorhynchus mykiss).

Pathological manifestations in rainbow trout (Oncorhynchus mykiss) following experimental waterborne infection with Yersinia ruckeri serotype O1 biotype 2 (strain 07111224) were investigated. Rainbow trout were exposed to 8 × 107  CFU/ml of Y. ruckeri by bath for 6 hr, and mortality was then monitored for 22 days post-infection (dpi). Organs were sampled at 3 dpi and also from moribund fish showing signs of severe systemic infection such as bleeding, exophthalmia or erratic swimming behaviour. Y. ruckeri was observed in the meninges and diencephalon of the brain, and lamina propria of olfactory organ at 3 dpi. At 12 dpi, Y. ruckeri had spread throughout the brain including cranial connective tissues and ventricles and the infection was associated with haemorrhages and an infiltration with leucocytes. Y. ruckeri infection and associated with leucocyte infiltration were observed at 13 dpi. In conclusion, Y. ruckeri strain 07111224 causes encephalitis in the acute phase of infection, which could explain why Y. ruckeri-affected fish show exophthalmia and erratic swimming known as signs of ERM.

Activation and Evasion of Inflammasomes by Yersinia.

The innate immune system plays an essential role in initiating the early response against microbial infection, as well as instructing and shaping subsequent responses. Microbial pathogens are enormously diverse in terms of the niches they occupy, their metabolic properties and requirements, and the cellular pathways that they target. Nevertheless, innate sensing of pathogens triggers a relatively stereotyped set of responses that involve transcriptional induction of key inflammatory mediators, as well as post-translational assembly and activation of a multiprotein inflammatory complex termed 'the inflammasome.' Along with classical Pattern Recognition Receptors, the inflammasome activation pathway has emerged as a key regulator of tissue homeostasis and immune defense. Components of the inflammasome generally exist within the cell in a soluble, monomeric state, and oligomerize in response to diverse enzymatic activities associated with infection or cellular stress. Inflammasome assembly triggers activation of the pro-enzyme caspase-1, resulting in the cleavage of caspase-1 targets. The most extensively studied targets are the cytokines of the IL-1 family, but the recent discovery of Gasdermin D as a novel target of caspase-1 and the related inflammatory caspase, caspase-11, has begun to mechanistically define the links between caspase-1 activation and cell death. Cell death is a hallmark of macrophage infection by many pathogens, including the gram-negative bacterial pathogens of the genus Yersinia. Intriguingly, the activities of the Yersinia-secreted effector proteins and the type III secretion system (T3SS) itself have been linked to both inflammasome activation and evasion during infection. The balance between these activating and inhibitory activities shapes the outcome of Yersinia infection. Here, we describe the current state of knowledge on interactions between Yersinia and the inflammasome system, with the goal of integrating these findings within the general framework of inflammasome responses to microbial pathogens.

Clinical aspects and self-reported symptoms of sequelae of Yersinia enterocolitica infections in a population-based study, Germany 2009-2010.

BACKGROUND: Foodborne Yersinia enterocolitica infections continue to be a public health problem in many countries. Consumption of raw or undercooked pork is the main risk factor for yersiniosis in Germany. Small children are most frequently affected by yersiniosis. In older children and young adults, symptoms of disease may resemble those of appendicitis and may lead to hospitalization and potentially unnecessary appendectomies. Y. enterocolitica infections may also cause sequelae such as reactive arthritis (ReA), erythema nodosum (EN), and conjunctivitis. METHODS: We studied clinical aspects of yersiniosis, antimicrobial use, and self-reported occurrence of appendectomies, reactive arthritis, erythema nodosum and conjunctivitis. To assess post-infectious sequelae participants of a large population-based case-control study on laboratory-confirmed Y. enterocolitica infections conducted in Germany in 2009-2010 were followed for 4 weeks. RESULTS: Diarrhea occurred most frequently in children ≤4 years (95%); abdominal pain in the lower right quadrant was most common in children 5-14 years of age (63%). Twenty-seven per cent of patients were hospitalized, 37% were treated with antimicrobials. In 6% of yersiniosis patients ≥5 years of age, appendectomies were performed. Self-reported symptoms consistent with ReA were reported by 12% of yersiniosis patients compared to 5% in a reference group not exposed to yersiniosis. Symptoms consistent with EN were reported by 3% of yersiniosis patients compared to 0.1% in the reference group. Symptoms of conjunctivitis occurred with the same frequency in yersiniosis patients and the reference group. CONCLUSIONS: Acute Y. enterocolitica infections cause considerable burden of illness with symptoms lasting for about 10 days and hospitalizations in more than a quarter of patients. The proportion of yersiniosis patients treated with antimicrobial drugs appears to be relatively high despite guidelines recommending their use only in severe cases. Appendectomies and post-infectious complications (ReA and EN) are more frequently reported in yersiniosis patients than in the reference group suggesting that they can be attributed to infections with Y. enterocolitica. Physicians should keep recent Y. enterocolitica infection in mind in patients with symptoms resembling appendicitis as well as in patients with symptoms of unclear arthritis.

No causal relationship between Yersinia enterocolitica infection and autoimmune thyroid disease: evidence from a prospective study.

The objective of this study was to evaluate prospectively the relationship between Yersinia enterocolitica (YE) infection and the development of overt autoimmune hypo- or hyperthyroidism (study A) and the de novo occurrence of thyroid antibodies (study B). This was a prospective cohort study of 790 euthyroid women who were first- or second-degree relatives of autoimmune thyroid disease (AITD) patients. Follow-up was 5 years, with annual assessments. Study A was a nested case-control study in which YE serological status was measured between cases {subjects who developed overt hypothyroidism [thyroid stimulating hormone (TSH) > 5·7 mU/l and free T4 (FT4) < 9·3 pmol/l] or overt hyperthyroidism (TSH < 0·4 mU/l and FT4 > 20·1 pmol/l)} and matched controls. For study B, 388 euthyroid women without thyroid antibodies at baseline were enrolled. The YE serological status was compared between subjects who developed thyroid peroxidase (TPO)-antibodies and/or thyroglobulin (Tg)-antibodies at 4-year follow-up and those who remained negative. For study A, the proportion of subjects positive for Yersinia enterocolitica outer membrane protein (YOP) immunoglobulin (Ig)G or YOP IgA did not differ between cases and controls at baseline. One year before the development of overt hypo- or hyperthyroidism, the proportion of subjects with YOP IgG was not different between cases and controls, but YOP IgA were less prevalent in cases. For study B, de novo occurrence of TPO (or TPO-antibodies and/or Tg-antibodies) did not differ between subjects in whom YOP IgG were positive or negative at baseline. Neither persistence nor emergence of YOP IgG at 4-year follow-up was associated with the occurrence of TPO-antibodies or Tg-antibodies. Similar results were observed with respect to YOP IgA. YE infection does not contribute to an increased risk of thyroid autoimmunity.

Yersinia enterocolitica targets cells of the innate and adaptive immune system by injection of Yops in a mouse infection model.

Yersinia enterocolitica (Ye) evades the immune system of the host by injection of Yersinia outer proteins (Yops) via a type three secretion system into host cells. In this study, a reporter system comprising a YopE-beta-lactamase hybrid protein and a fluorescent staining sensitive to beta-lactamase cleavage was used to track Yop injection in cell culture and in an experimental Ye mouse infection model. Experiments with GD25, GD25-beta1A, and HeLa cells demonstrated that beta1-integrins and RhoGTPases play a role for Yop injection. As demonstrated by infection of splenocyte suspensions in vitro, injection of Yops appears to occur randomly into all types of leukocytes. In contrast, upon infection of mice, Yop injection was detected in 13% of F4/80(+), 11% of CD11c(+), 7% of CD49b(+), 5% of Gr1(+) cells, 2.3% of CD19(+), and 2.6% of CD3(+) cells. Taking the different abundance of these cell types in the spleen into account, the highest total number of Yop-injected cells represents B cells, particularly CD19(+)CD21(+)CD23(+) follicular B cells, followed by neutrophils, dendritic cells, and macrophages, suggesting a distinct cellular tropism of Ye. Yop-injected B cells displayed a significantly increased expression of CD69 compared to non-Yop-injected B cells, indicating activation of these cells by Ye. Infection of IFN-gammaR (receptor)- and TNFRp55-deficient mice resulted in increased numbers of Yop-injected spleen cells for yet unknown reasons. The YopE-beta-lactamase hybrid protein reporter system provides new insights into the modulation of host cell and immune responses by Ye Yops.

Yersinia lead SUMO attack.

Little is known about the mechanism by which Yops, proteins that Yersinia inject into the cytosol of macrophage, cause downregulation of the inflammatory response and diseases such as the plague. Now it appears that Yops are the first bacterial member of a new family of ubiquitin-like proteases.

Transition from interleukin 1 beta (IL-1 beta) to IL-1 alpha production during maturation of inflammatory macrophages in vivo.

In situ production of interleukin 1 alpha (IL-1 alpha) and IL-1 beta was investigated in Peyer's patches (PP) of mice undergoing an acute bacterial infection with Yersinia enterocolitica O8. Synthesis of IL-1 beta, as determined by immunohistochemistry, was found primarily in monocytes migrating into the inflamed PP. In comparison, synthesis of IL-1 alpha was temporarily delayed by at least 24 h and was only found in mature macrophages, which did not produce detectable levels of IL-1 beta. This indicates a transition from IL-1 beta to IL-1 alpha production during maturation of monocytes into inflammatory macrophages, and further emphasizes a dichotomy between IL-1 alpha and IL-1 beta.

Yersinia type III secretion: send in the effectors.

Pathogenic Yersinia spp (Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica) have evolved an exquisite method for delivering powerful effectors into cells of the host immune system where they inhibit signaling cascades and block the cells' response to infection. Understanding the molecular mechanisms of this system has provided insight into the processes of phagocytosis and inflammation.

The elusive activity of the Yersinia protein kinase A kinase domain is revealed.

Yersinia spp. pathogens use their type III secretion system to translocate effectors that manipulate host signaling pathways during infection. Although molecular targets for five of the six known Yersinia effectors are known, the target for the serine/threonine kinase domain of Yersinia protein kinase A (YpkA) has remained elusive. Recently, Navarro et al. (2007) demonstrated that YpkA phosphorylates Galphaq, and inhibits Galphaq-mediated signaling. Inhibition by YpkA could contribute to one of the most documented symptoms of Yersinia pestis infection, extensive bleeding.

Bacteria induce CTGF and CYR61 expression in epithelial cells in a lysophosphatidic acid receptor-dependent manner.

Cysteine-rich protein 61 (Cyr61/CCN1) and connective tissue growth factor (CTGF/CCN2) are members of the CCN (CYR61, CTGF, nephroblastoma overexpressed gene) family and exert pleiotropic functions such as regulation of adhesion, migration, extracellular matrix deposition, or cell differentiation, and play an important role in wound healing. This study focused on the nature of the so far unknown CTGF and CYR61 mRNA expression of epithelial cells after infection with bacteria. We demonstrate that infection of epithelial cells with attenuated Yersinia enterocolitica lacking the virulence plasmid pYV leads to the expression of CYR61 and CTGF. Virulent Y. enterocolitica bearing the pYV virulence plasmid suppressed the mRNA expression of these genes. Yersinia-mediated inhibition of CTGF and CYR61 mRNA expression is partially mediated by the cysteine protease YopT. Further characterization of the Yersinia factors, which trigger CTGF and CYR61 mRNA expression, demonstrated that these factors were secreted and could be enriched in lipid extracts. Beside Yersinia, several other bacteria such as Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, or Staphylococcus aureus, as well as supernatants of these bacteria induced CTGF and CYR61 expression. Blocking experiments with the lysophosphatidic acid (LPA) receptor-specific inhibitor Ki16425 suggest a general involvement of LPA receptors in bacteria-triggered CTGF and CYR61 expression. These data suggest that LPA receptor-dependent expression of CTGF and CYR61 represents a common host response after interaction with bacteria.

The Infection Process of Yersinia ruckeri: Reviewing the Pieces of the Jigsaw Puzzle.

Finding the keys to understanding the infectious process of Yersinia ruckeri was not a priority for many years due to the prompt development of an effective biotype 1 vaccine which was used mainly in Europe and USA. However, the gradual emergence of outbreaks in vaccinated fish, which have been reported since 2003, has awakened interest in the mechanism of virulence in this pathogen. Thus, during the last two decades, a large number of studies have considerably enriched our knowledge of many aspects of the pathogen and its interaction with the host. By means of both conventional and a variety of novel strategies, such as cell GFP tagging, bioluminescence imaging and optical projection tomography, it has been possible to determine three putative Y. ruckeri infection routes, the main point of entry for the bacterium being the gill lamellae. Moreover, a wide range of potential virulence factors have been highlighted by specific gene mutagenesis strategies or genome-wide transposon/plasmid insertion-based screening approaches, such us in vivo expression technology (IVET) and signature tagged mutagenesis (STM). Finally, recent proteomic and whole genomic analyses have allowed many of the genes and systems that are potentially implicated in the organism's pathogenicity and its adaptation to the host environmental conditions to be elucidated. Altogether, these studies contribute to a better understanding of the infectious process of Y. ruckeri in fish, which is crucial for the development of more effective strategies for preventing or treating enteric redmouth disease (ERM).

Faecal shedding of pathogenic Yersinia enterocolitica determined by qPCR for yst virulence gene is associated with reduced live weight but not diarrhoea in prime lambs.

Associations between faecal shedding of pathogenic Yersinia enterocolitica (based on the yst virulence gene) with growth, carcass weight and diarrhoea were investigated using an observational longitudinal study of 1200 crossbred prime (meat) lambs on eight Australian farms. Live weight, breech faecal soiling score (scale 1-5) and faecal consistency score (FCS; scale 1-5) were recorded, and faecal samples collected from each lamb on three sampling occasions; weaning (≈12 weeks of age), post-weaning (≈19 weeks) and pre-slaughter (≈29 weeks). Hot standard carcass weight was measured at slaughter. Faecal samples were screened for presence and concentration of pathogenic Y. enterocolitica using quantitative PCR. Associations of pathogenic Y. enterocolitica detection and shedding intensity with lamb health and production were assessed using general linear models (carcass weight), linear mixed effects models (live weight, FCS and breech soiling score) and non-parametric tests (FCS and breech soiling score). Prevalence for non-pelleted faeces (FCS ≥ 3.0) and diarrhoea (FCS ≥ 4.0) were compared with the two-tailed z-test, odds ratios and relative risk. Lambs shedding pathogenic Y. enterocolitica were 3.78 kg lighter post-weaning (P < 0.001) and 2.61 kg lighter pre-slaughter (P = 0.035) compared to lambs in which pathogenic Y. enterocolitica was not detected. Higher faecal concentration of pathogenic Y. enterocolitica was associated with lower live weight (P < 0.001). There was no association between pathogenic Y. enterocolitica detection and carcass weight. Overall, there was no evidence of association between pathogenic Y. enterocolitica detection and diarrhoea (higher FCS, higher risk for non-pelleted faeces or diarrhoea, or higher breech soiling score). Only one flock had increased relative risk for non-pelleted faeces associated with pathogenic Y. enterocolitica detection, and one other flock had increased relative risk for diarrhoea associated with pathogenic Y. enterocolitica detection. This is the first report of an association between reduced sheep live weight and pathogenic Y. enterocolitica based on the presence of the yst gene for heat stable enterotoxin determined by qPCR in sheep. Notably, impacts on live weight were observed in the absence of diarrhoea.

[Extracellular resistance of Yersinia pestis to phagocytosis].

The authors were the first to perform stimulation of parasitizing condition of plague bacilli in mammalian bloodstream by addition of adequate quantity of glucose and calcium ions into the routine bacteriological medium, as well as growing the plague agent in RPMI-1640, isotonic to the serum of man and mammals susceptible to plague. Comparison of proliferative, phenotypic, and biochemical properties of fully virulent and vaccine Y. pestis strains demonstrated the advantages of RPMI-1640 medium, which provided extensive in vitro multiplication of the mentioned microorganisms similar to the bacterioemic stage of plague. Using methods of molecular microbiology and immunology, including a panel of monoclonal antibodies, the researchers demonstrated an abrupt fall of production of main plague surface species-specific antigens such as F1, 'murine' toxin/phospholipase D and fibrinolysin, followed by inhibition of biochemical activities associated with these antigenic substances in Y. pestis, as well as specific components of lipopolysaccharide. Possible molecular mechanisms of virulence and adaptive variability of plague bacteria in the extracellular conditions in mammalian organism are discussed.

Human Yersinia enterocolitica infections in Wisconsin. Clinical, laboratory and epidemiologic features.

Yersinia enterocolitica has been sought in stool and blood culture specimens by the Wisconsin State Laboratory of Hygiene (SLH) since 1973. Clinical information on symptoms, duration of illness, and use of antibiotics for 41 persons with Y. enterocolitica infections from January 1, 1979, to September 30, 1980, was obtained by telephone interviews. Diarrhea and abdominal pain were the most common symptoms of the ill persons; extraintestinal symptoms were infrequently reported. Ten infected persons (24 percent) had no illness. Review of a 10 percent sample of all stool specimens cultured at the SLH from June 20, 1977, to June 20, 1979, revealed that Salmonella was the most commonly isolated enteric pathogen (15.4 percent) followed by Shigella (2.0 percent) and Y. enterocolitica (0.7 percent). Several different biotypes and serotypes of Y. enterocolitica were associated with illness. Y. enterocolitica isolates were uniformly susceptible to a wide variety of antibiotics, and most isolates were resistant to ampicillin. Epidemiologic studies showed that persons with Y. enterocolitica infections were more likely to live in rural counties than were all persons sending stool samples or those having Salmonella infections; underlying illness was identified as a risk factor for infection.

Yersinia enterocolitica infection in children.

The clinical presentation, course and outcome of Yersinia enterocolitica infection was studied prospectively in 125 children. Enteric forms occurred in 114 children (92 enteritis, 20 pseudoappendicitis, 2 chronic ileitis), of whom 17 also had extramesenteric manifestations; 11 children had one or more extramesenteric forms without enteric disease. Enteritis occurred more frequently in young children whereas serious forms and extramesenteric forms were more common in children older than 6 years of age (P < 0.001). Arthritis was observed in 13 children and extensive lymphadenopathy in 11; 1 child had septicemia with pleurisy, 1 had vasculitis, 1 had cholecystitis and 4 had erythema nodosum. Diagnosis was established by positive culture in 100 (80%) children and by agglutinin test in 11 of 45 (24%), demonstration of circulating specific anti-IgA and anti-IgG to Yersinia outer membrane proteins in 47 of 48 (98%) and detection of antigen in biopsies in 28 of 33 (85%) children. The 2 latter methods were superior to the agglutinin test. Serotype O3 and O9 predominated. The frequency and seriousness of complications may justify the use of antibiotics for Yersinia enteritis in children 6 years of age or older.

Yersinia enterocolitica infection in children.

BACKGROUND: Yersinia enterocolitica can cause illness ranging from self-limited enteritis to life-threatening systemic infection. The present study was undertaken to review the epidemiology, clinical manifestations, complications and outcome of Y. enterocolitica enteritis in children seen at a large children's hospital. METHODS: The project consisted of a retrospective chart review of medical and microbiologic records of all children with stool cultures positive for Y. enterocolitica during a 7-year period. RESULTS: The review included 142 patients with Y. enterocolitica enteritis. Patients' ages ranged from 18 days to 12 years, and the majority (85%) were younger than 1 year. Most patients presented during November, December and January. History of exposure to chitterlings (raw pork intestines) at home was elicited in 25 of 30 cases. Y. enterocolitica accounted for 12.6% (142 of 1,120) of all bacterial intestinal pathogens isolated during the study period. Blood cultures were positive in 7(9%) of 78 patients; 6 were younger than 1 year and one 12-year-old had sickle cell disease. Of 132 isolates tested all were susceptible to trimethoprim-sulfamethoxazole, tobramycin and gentamicin; the majority were susceptible to cefotaxime (99%), ceftazidime (89%) and cefuroxime (88%). All bacteremic patients responded to cefotaxime treatment. Follow-up evaluation of 40 ambulatory patients revealed no difference in clinical improvement between those treated with oral trimethoprim-sulfamethoxazole (17 of 23) and those who were not treated (8 of 17) (P = 0.1). CONCLUSION: Y. enterocolitica is an important cause of enteritis in our young patient population during the winter holidays. Exposure of infants to chitterlings appears to be a risk factor. Infants younger than 3 months are at increased risk for bacteremia. Cefotaxime is effective in the treatment of Y. enterocolitica bacteremia; however, the role of oral antibiotics in the management of enteritis needs further evaluation.

Prospective study of Yersinia enterocolitica infection in thalassemic patients.

We determined prospectively during a 12-month period the incidence, clinical characteristics and outcome of Yersinia enterocolitica infection in 144 thalassemic patients (mean age, 12.8 years) and compared them with 100 controls (mean age, 12.1 years). Symptomatic Y. enterocolitica infection occurred in 14 (10%) of the thalassemic patients and in 2 (2%) controls (P = 0.017). Of the 14 thalassemic patients 5 (36%) had septicemia and 9 (64%) had focal infection (enteritis in 8 and tonsillitis in 1). One control patient had acute enteritis and the other had tonsillitis. All isolates from these patients belonged to pathogenic phenotypes of Y. enterocolitica. Pending culture results symptomatic thalassemic patients discontinued treatment with deferoxamine and were treated with intravenous antibiotic therapy. Patients with the ultimate diagnosis of focal Y. enterocolitica infection continued treatment with intramuscular ceftriaxone or intravenous trimethoprim/sulfamethoxazole (TMP/SMX) for 7 days, whereas those with septicemia continued treatment with intravenous TMP/SMX for 14 days. The outcome was favorable in all 14 thalassemic patients. We conclude that Y. enterocolitica is a significant cause of morbidity in our patients with thalassemia and that prompt antibiotic therapy might prevent life-threatening conditions as well as a complicated course with long term sequelae.

Proper expression of the O-antigen of lipopolysaccharide is essential for the virulence of Yersinia enterocolitica O:8 in experimental oral infection of rabbits.

The O-antigen of lipopolysaccharide (LPS) is required for virulence in Yersinia enterocolitica serotype O:8. Here we evaluated the importance of controlling the O-antigen biosynthesis using an in vivo rabbit model of infection. Y. enterocolitica O:8 wild-type strain was compared to three mutants differing in the O-antigen phenotype: (i) the rough strain completely devoid of the O-antigen, (ii) the wzy strain that lacks the O-antigen polymerase (Wzy protein) and expresses LPS with only one repeat unit, and (iii) the wzz strain that lacks the O-antigen chain length determinant (Wzz protein) and expresses LPS without modal distribution of O-antigen chain lengths. The most attenuated strain was the wzz mutant. The wzz bacteria were cleared from the tissues by day 30, the blood parameters were least dramatic and histologically only immunomorphological findings were seen. The level of attenuation of the rough and the wzy strain bacteria was between the wild-type and the wzz strain. Wild-type bacteria were highly resistant to killing by polymorphonuclear leukocytes, the wzz strain bacteria were most sensitive and the rough and wzy strain bacteria were intermediate resistant. These results clearly demonstrated that the presence of O-antigen on the bacterial surface is not alone sufficient for full virulence, but also there is a requirement for its controlled chain length.