Loss of CNFY toxin-induced inflammation drives Yersinia pseudotuberculosis into persistency

Gastrointestinal infections caused by enteric yersiniae can become persistent and complicated by relapsing enteritis and severe autoimmune disorders. To establish a persistent infection, the bacteria have to cope with hostile surroundings when they transmigrate through the intestinal epithelium and colonize underlying gut-associated lymphatic tissues. How the bacteria gain a foothold in the face of host immune responses is poorly understood. Here, we show that the CNFY toxin, which enhances translocation of the antiphagocytic Yop effectors, induces inflammatory responses. This results in extensive tissue destruction, alteration of the intestinal microbiota and bacterial clearance. Suppression of CNFY function, however, increases interferon-γ-mediated responses, comprising non-inflammatory antimicrobial activities and tolerogenesis. This process is accompanied by a preterm reprogramming of the pathogen's transcriptional response towards persistence, which gives the bacteria a fitness edge against host responses and facilitates establishment of a commensal-type life style.

Dissociation of Tissue Destruction and Bacterial Expansion during Bubonic Plague

Activation and/or recruitment of the host plasmin, a fibrinolytic enzyme also active on extracellular matrix components, is a common invasive strategy of bacterial pathogens. Yersinia pestis, the bubonic plague agent, expresses the multifunctional surface protease Pla, which activates plasmin and inactivates fibrinolysis inhibitors. Pla is encoded by the pPla plasmid. Following intradermal inoculation, Y. pestis has the capacity to multiply in and cause destruction of the lymph node (LN) draining the entry site. The closely related, pPla-negative, Y. pseudotuberculosis species lacks this capacity. We hypothesized that tissue damage and bacterial multiplication occurring in the LN during bubonic plague were linked and both driven by pPla. Using a set of pPla-positive and pPla-negative Y. pestis and Y. pseudotuberculosis strains in a mouse model of intradermal injection, we found that pPla is not required for bacterial translocation to the LN. We also observed that a pPla-cured Y. pestis caused the same extensive histological lesions as the wild type strain. Furthermore, the Y. pseudotuberculosis histological pattern, characterized by infectious foci limited by inflammatory cell infiltrates with normal tissue density and follicular organization, was unchanged after introduction of pPla. However, the presence of pPla enabled Y. pseudotuberculosis to increase its bacterial load up to that of Y. pestis. Similarly, lack of pPla strongly reduced Y. pestis titers in LNs of infected mice. This pPla-mediated enhancing effect on bacterial load was directly dependent on the proteolytic activity of Pla. Immunohistochemistry of Pla-negative Y. pestis-infected LNs revealed extensive bacterial lysis, unlike the numerous, apparently intact, microorganisms seen in wild type Y. pestis-infected preparations. Therefore, our study demonstrates that tissue destruction and bacterial survival/multiplication are dissociated in the bubo and that the primary action of Pla is to protect bacteria from destruction rather than to alter the tissue environment to favor Y. pestis propagation in the host.

The hallmark of bubonic plague, a disease that ravaged Medieval Europe and is still prevalent in several countries, is the bubo, a highly inflammatory and painful lymph node, which is characterized by high concentrations of bacteria within a severely damaged organ. Yersinia pestis, the causative agent, expresses a surface protease, Pla, critical to the development of bubonic plague. This multitarget protease has the potential to activate the fibrinolytic pathway and to promote destruction of extracellular protein networks within tissues. Hence, it was expected that Pla was responsible for the tissue destructions of the bubo, and consequently, for bacterial propagation and virulence. However, we found, using various engineered Yersinia strains in a mouse model of bubonic plague, that Pla proteolytic activity was dispensable for lymph node alteration, but was required to achieve high bacterial loads in the organ. Further analysis showed that Pla is essential for preventing the bacteria from being destroyed in the host. Therefore, the role of Pla as a virulence factor is to protect Y. pestis survival and integrity in the host, rather than to assist its spread through tissue destruction.

Natural Killer Cells Mediate Protection against Yersinia pseudotuberculosis in the Mesenteric Lymph Nodes

Natural killer cells play a crucial role in the initial defense against bacterial pathogens. The crosstalk between host cells infected with intracellular pathogens and NK cells has been studied intensively, but not much attention has been given to characterize the role of NK cells in the response to extracellular bacterial pathogens such as yersiniae. In this study we used antibody-mediated NK cell depletion to address the importance of this immune cell type in controlling a Y. pseudotuberculosis infection. Analysis of the bacterial counts was used to follow the infection and flow cytometry was performed to characterize the composition and dynamic of immune cells. Depletion of NK cells led to higher bacterial loads within the mesenteric lymph nodes. We further show that in particular CD11b⁺ CD27⁺ NK cells which express higher levels of the activation marker CD69 increase within the mesenteric lymph nodes during a Y. pseudotuberculosis infection. Moreover, in response to the activation NK cells secrete higher levels of IFNy, which in turn triggers the production of the proinflammatory cytokine TNFα. These results suggest, that NK cells aid in the clearance of Y. pseudotuberculosis infections mainly by triggering the expression of proinflammatory cytokines manipulating the host immune response.

[CHARACTERISTICS OF FORMATION, INHIBITION AND DESTRUCTION OF YERSINIA PSEUDOTUBERCULOSIS BIOFILMS FORMING ON ABIOTIC SURFACES]

AIM

Detection of conditions of Yersinia pseudotuberculosis biofilm formation, their quantitative testing.

MATERIALS AND METHODS

Y. pseudotuberculosis strains, nutrient media, standard 96-well polystyrene plates, crystal violet dye as well as bacteriologic, spectrophotometric, statistical methods were used.

RESULTS

All the studied Y pseudotuberculosis strains formed a well expressed biofilm on abiotic surface during cultivation of bacteria in 200 µl of a plate well at a temperature of 20-22°C for 4-7 days. Bacteria CFU number in biofilm reduced by day 10 of incubation. DNAse I was found to inhibit biofilm formation, and also partially destroyed mature Y. pseudotuberculosis biofilm. The presence of DNA in extra-cellular matrix of biofilm was shown.

CONCLUSION

An ability of Y. pseudotuberculosis to form biofilm on abiotic surface was established. The conditions of biofilm formation were determined. Inhibiting effect of DNAse I on Y. pseudotuberculosis was shown.

IscR is essential for yersinia pseudotuberculosis type III secretion and virulence

Type III secretion systems (T3SS) are essential for virulence in dozens of pathogens, but are not required for growth outside the host. Therefore, the T3SS of many bacterial species are under tight regulatory control. To increase our understanding of the molecular mechanisms behind T3SS regulation, we performed a transposon screen to identify genes important for T3SS function in the food-borne pathogen Yersinia pseudotuberculosis. We identified two unique transposon insertions in YPTB2860, a gene that displays 79% identity with the E. coliiron-sulfur cluster regulator, IscR. A Y. pseudotuberculosis iscR in-frame deletion mutant (ΔiscR) was deficient in secretion of Ysc T3SS effector proteins and in targeting macrophages through the T3SS. To determine the mechanism behind IscR control of the Ysc T3SS, we carried out transcriptome and bioinformatic analysis to identify Y. pseudotuberculosis genes regulated by IscR. We discovered a putative IscR binding motif upstream of the Y. pseudotuberculosis yscW-lcrF operon. As LcrF controls transcription of a number of critical T3SS genes in Yersinia, we hypothesized that Yersinia IscR may control the Ysc T3SS through LcrF. Indeed, purified IscR bound to the identified yscW-lcrF promoter motif and mRNA levels of lcrF and 24 other T3SS genes were reduced in Y. pseudotuberculosis in the absence of IscR. Importantly, mice orally infected with the Y. pseudotuberculosis ΔiscR mutant displayed decreased bacterial burden in Peyer's patches, mesenteric lymph nodes, spleens, and livers, indicating an essential role for IscR in Y. pseudotuberculosis virulence. This study presents the first characterization of Yersinia IscR and provides evidence that IscR is critical for virulence and type III secretion through direct regulation of the T3SS master regulator, LcrF.

Bacterial pathogens use regulators that sense environmental cues to enhance their fitness. Here, we identify a transcriptional regulator in the human gut pathogen, Yersinia pseudotuberculosis, which controls a specialized secretion system essential for bacterial growth in mammalian tissues. This regulator was shown in other bacterial species to alter its activity in response to changes in iron concentration and oxidative stress, but has never been studied in Yersinia. Importantly, Y. pseudotuberculosis experiences large changes in iron bioavailability upon transit from the gut to deeper tissues and iron is a critical component in Yersinia virulence, as individuals with iron overload disorders have enhanced susceptibility to systemic Yersinia infections. Our work places this iron-modulated transcriptional regulator within the regulatory network that controls virulence gene expression in Y. pseudotuberculosis, identifying it as a potential new target for antimicrobial agents.

The cytotoxic necrotizing factor of Yersinia pseudotuberculosis (CNFY) enhances inflammation and Yop delivery during infection by activation of Rho GTPases

Some isolates of Yersinia pseudotuberculosis produce the cytotoxic necrotizing factor (CNF_Y), but the functional consequences of this toxin for host-pathogen interactions during the infection are unknown. In the present study we show that CNF_Y has a strong influence on virulence. We demonstrate that the CNF_Y toxin is thermo-regulated and highly expressed in all colonized lymphatic tissues and organs of orally infected mice. Most strikingly, we found that a cnfY knock-out variant of a naturally toxin-expressing Y. pseudotuberculosis isolate is strongly impaired in its ability to disseminate into the mesenteric lymph nodes, liver and spleen, and has fully lost its lethality. The CNF_Y toxin contributes significantly to the induction of acute inflammatory responses and to the formation of necrotic areas in infected tissues. The analysis of the host immune response demonstrated that presence of CNF_Y leads to a strong reduction of professional phagocytes and natural killer cells in particular in the spleen, whereas loss of the toxin allows efficient tissue infiltration of these immune cells and rapid killing of the pathogen. Addition of purified CNF_Y triggers formation of actin-rich membrane ruffles and filopodia, which correlates with the activation of the Rho GTPases, RhoA, Rac1 and Cdc42. The analysis of type III effector delivery into epithelial and immune cells in vitro and during the course of the infection further demonstrated that CNF_Y enhances the Yop translocation process and supports a role for the toxin in the suppression of the antibacterial host response. In summary, we highlight the importance of CNF_Y for pathogenicity by showing that this toxin modulates inflammatory responses, protects the bacteria from attacks of innate immune effectors and enhances the severity of a Yersinia infection.

Various toxins and effector proteins of bacterial pathogens have been found to manipulate eukaryotic cell machineries to promote persistence and proliferation within their hosts. Many of these virulence factors target small Rho GTPases, but their role in pathogenesis is often unknown. Here, we addressed the expression and functional consequences of the CNF_Y toxin found in some isolates of Y. pseudotuberculosis. We found that CNF_Y besides modulating the cell cytoskeleton by activation of the GTPases RhoA, Rac1 and Cdc42, contributes to increased inflammation and tissue damage. Moreover, CNF_Y increases the ability of Yersinia to prevent the attack of the immune system, by enhancing the delivery of antiphagocytic and cytotoxic effectors into professional phagocytes. Our findings provide the first insights into the multi-functional action and severe consequences of the CNF_Y toxin on the inflammatory response and disease-associated tissue damage during the natural course of the infection.

Adhesins and host serum factors drive Yop translocation by yersinia into professional phagocytes during animal infection

Yersinia delivers Yops into numerous types of cultured cells, but predominantly into professional phagocytes and B cells during animal infection. The basis for this cellular tropism during animal infection is not understood. This work demonstrates that efficient and specific Yop translocation into phagocytes by Yersinia pseudotuberculosis (Yptb) is a multi-factorial process requiring several adhesins and host complement. When WT Yptb or a multiple adhesin mutant strain, ΔailΔinvΔyadA, colonized tissues to comparable levels, ΔailΔinvΔyadA translocated Yops into significantly fewer cells, demonstrating that these adhesins are critical for translocation into high numbers of cells. However, phagocytes were still selectively targeted for translocation, indicating that other bacterial and/or host factors contribute to this function. Complement depletion showed that complement-restricted infection by ΔailΔinvΔyadA but not WT, indicating that adhesins disarm complement in mice either by prevention of opsonophagocytosis or by suppressing production of pro-inflammatory cytokines. Furthermore, in the absence of the three adhesins and complement, the spectrum of cells targeted for translocation was significantly altered, indicating that Yersinia adhesins and complement direct Yop translocation into neutrophils during animal infection. In summary, these findings demonstrate that in infected tissues, Yersinia uses adhesins both to disarm complement-dependent killing and to efficiently translocate Yops into phagocytes.

Many bacterial pathogens use a needle-like structure to deliver proteins into host cells to cause disease. Yersinia species use one such structure, called a type III secretion system, to deliver a set of 6–7 proteins, called Yops, into host cells. These Yops act to dismantle host defenses and establish infection. Bacterial adhesins and host factors have been suggested to promote proper delivery of Yops into specific mammalian cells. We identify three Yersinia pseudotuberculosis adhesins that significantly contribute to bacterial survival and efficient Yop delivery into host cells during animal infection. We also demonstrate that host serum factors in combination with Yersinia adhesins contribute to the number of cells that are injected with Yops and to the specific cell types targeted for injection. Our study illustrates that bacterial adhesins and host factors contribute to efficient delivery of effector proteins into targeted host cells during infection.

[The new views to pseudotuberculosis pathology]

For the first time the nature of cell damages under pseudotuberculosis as a generalized infection has been analyzed by positions of the modern knowledge about types of the cell death. The own and literature data have pointed to presence the apoptosis-induced effect of Yersinia pseudotuberculosis, a causative agent of this infection. In conclusion, the typical pathological changes for pseudotuberculosis infection such as granuloma formation with the central karyorrhexis could be appearance of apoptotic and secondary necrotic changes.

[Clinicoimmunological monitoring of therapy in patients with associated forms of yersiniosis]

Characteristics of the clinical process and immunological profile in children with yersiniosis as a monoinfection or in association with acute intenstinal infections and virus hepatitis A are presented. The efficacy of the immunotropic therapy with cycloferon, an interferon inductor, and recombinant interferon in the patients with the viral and bacterial association of the disease (yersiniosis + hepatitis A) and initial disbalance of the serum cytokines was estimated. Dependence of the interferon clinicolaboratory efficacy on the initial levels of serum y-interferon, IL2 and IIA, promoting shorter terms of hyperthermia, diarrhea syndrome and cytolysis syndrome was shown. It allowed to optimize the scheme of the pathogenetic therapy of Yersinia mixed infection.

Reduced secretion of YopJ by Yersinia limits in vivo cell death but enhances bacterial virulence

Numerous microbial pathogens modulate or interfere with cell death pathways in cultured cells. However, the precise role of host cell death during in vivo infection remains poorly understood. Macrophages infected by pathogenic species of Yersinia typically undergo an apoptotic cell death. This is due to the activity of a Type III secreted effector protein, designated YopJ in Y. pseudotuberculosis and Y. pestis, and YopP in the closely related Y. enterocolitica. It has recently been reported that Y. enterocolitica YopP shows intrinsically greater capacity for being secreted than Y. pestis YopJ, and that this correlates with enhanced cytotoxicity observed for high virulence serotypes of Y. enterocolitica. The enzymatic activity and secretory capacity of YopP from different Y. enterocolitica serotypes have been shown to be variable. However, the underlying basis for differential secretion of YopJ/YopP, and whether reduced secretion of YopJ by Y. pestis plays a role in pathogenesis during in vivo infection, is not currently known. It has also been reported that similar to macrophages, Y. enterocolitica infection of dendritic cells leads to YopP-dependent cell death. We demonstrate here that in contrast to Y. enterocolitica, Y. pseudotuberculosis infection of bone marrow–derived dendritic cells does not lead to increased cell death. However, death of Y. pseudotuberculosis–infected dendritic cells is enhanced by ectopic expression of YopP in place of YopJ. We further show that polymorphisms at the N-terminus of the YopP/YopJ proteins are responsible for their differential secretion, translocation, and consequent cytotoxicity. Mutation of two amino acids in YopJ markedly enhanced both translocation and cytotoxicity. Surprisingly, expression of YopP or a hypersecreted mutant of YopJ in Y. pseudotuberculosis resulted in its attenuation in oral mouse infection. Complete absence of YopJ also resulted in attenuation of virulence, in accordance with previous observations. These findings suggest that control of cytotoxicity is an important virulence property for Y. pseudotuberculosis, and that intermediate levels of YopJ-mediated cytotoxicity are necessary for maximal systemic virulence of this bacterial pathogen.

The ability of bacterial pathogens to modulate death of infected host cells is an important virulence determinant. For pathogenic members of the genus Yersinia, the type III secreted effector protein YopJ/YopP is required for Yersinia-induced macrophage death. The YopJ protein is expressed by Y. pseudotuberculosis, while the ninety-four percent identical YopP protein is expressed by Y. enterocolitica. Y. enterocolitica infection also triggers YopP-dependent killing of dendritic cells, which are critical antigen presenting cells of the immune system. We demonstrate that in contrast to macrophages, dendritic cells are resistant to Y. pseudotuberculosis-mediated cytotoxicity. However, Y. pseudotuberculosis expressing YopP in place of YopJ was highly cytotoxic toward dendritic cells. This difference in cytotoxicity was attributable to a difference in the delivery of YopJ and YopP into mammalian cells. Furthermore, mutation of two amino acids at the N-terminus of YopJ enhanced its delivery and cytotoxicity. Remarkably, we found that enhancing the cytotoxicity of Y. pseudotuberculosis by expression of YopP led to its attenuation in a mouse model of Yersinia infection. This indicates that optimal virulence for a given pathogen requires careful regulation of virulence properties and highlights the potential evolutionary tradeoffs between cellular cytotoxicity and in vivo virulence.

[Clinicomorphologic observation of Yersinia infection]

The paper describes a unique case of lingering (8-month) generalized Yersinia infection (pseudotuberculosis) caused by Yersinia pseudotuberculosis serovar 3. The postmortem diagnosis could be established using immunomorphological techniques. Based on the described case and the data available in the literature, the authors discuss the similarity of pathomorphological changes and the possible etiological community of Crohn's disease.

Intranasal inoculation of mice with Yersinia pseudotuberculosis causes a lethal lung infection that is dependent on Yersinia outer proteins and PhoP

Yersinia pseudotuberculosis infects many mammals and birds including humans, livestock, and wild rodents and can be recovered from the lungs of infected animals. To determine the Y. pseudotuberculosis factors important for growth during lung infection, we developed an intranasal model of infection in mice. Following intranasal inoculation, we monitored both bacterial growth in lungs and dissemination to systemic tissues. Intranasal inoculation with as few as 18 CFU of Y. pseudotuberculosis caused a lethal lung infection in some mice. Over the course of 7 days, wild-type Y. pseudotuberculosis replicated to nearly 1 x 10(8) CFU/g of lung in BALB/c mice, induced histopathology in lungs consistent with pneumonia, but disseminated sporadically to other tissues. In contrast, a Delta yopB deletion strain was attenuated in this model, indicating that translocation of Yersinia outer proteins (Yops) is essential for virulence. Additionally, a Delta yopH null mutant failed to grow to wild-type levels by 4 days postintranasal inoculation, but deletions of any other single effector YOP did not attenuate lung colonization 4 days postinfection. Strains with deletions in yopH and any one of the other known effector yop genes were more attenuated that the Delta yopH strain, indicating a unique role for yopH in lungs. In summary, we have characterized the progression of a lung infection with an enteric Yersinia pathogen and shown that YopB and YopH are important in lung colonization and dissemination. Furthermore, this lung infection model with Y. pseudotuberculosis can be used to test potential therapeutics against Yersinia and other gram-negative infections in lungs.

Hepatic yersiniosis in a cougar (Felis concolor)

A cougar (Felis concolor) was diagnosed with hepatic yersiniosis by bacterial culture and histopathology. The animal had a 2-week history of anorexia and jaundice before its death. Grossly, the liver exhibited caseo-necrotic foci. Histopathologically, there was necrotizing and suppurative hepatitis, with large numbers of intralesional gram-negative coccobacilli. Additional hepatic lesions included central vein thrombosis, lymphoplasmacytic portal hepatitis, and capsulitis. Yersinia pseudotuberculosis coccobacilli were isolated in pure culture from the hepatic lesions. Because the hepatic lesions in this animal resemble those of other zoonotic diseases, such as plague and tularemia, veterinarians and laboratory personnel who handle samples should take adequate safety precautions. This report is the first to describe the pathology associated with hepatic yersiniosis in a cougar.

Yersinia pseudotuberculosis adhesins regulate tissue-specific colonization and immune cell localization in a mouse model of systemic infection

Yersinia pseudotuberculosis mutants deficient for the adhesins invasin and/or YadA were injected intravenously into BALB/c mice. Invasin expression inhibited colonization of the liver and spleen. YadA decreased liver colonization but promoted growth within the lung. The persistence of leukocytes within liver microabscesses correlated with enhanced colonization and lack of adhesin expression.

A non-invasive quantitative assay to measure murine intestinal inflammation using the neutrophil marker lactoferrin

Intestinal inflammation in mice is most frequently assessed by histology or FACS, processes that necessitate sacrificing mice. We developed a lactoferrin ELISA for murine feces to quantify intestinal inflammation in mice with enteric infections or colitis. Levels of fecal lactoferrin, a protein secreted by activated neutrophils, were consistent with neutrophil infiltration as assessed by histology, indicating that this fecal lactoferrin ELISA is a good alternative to histology. The fecal lactoferrin ELISA provides a non-invasive, quantitative assessment of intestinal inflammation, which should facilitate longitudinal studies of the development of and/or therapies reducing intestinal inflammation in individual mice and reduce the number of mice needed for such studies.

Critical role of T cell migration in bacterial superantigen-mediated shock in mice

Bacterial superantigens have been implicated in the pathogenesis of several human diseases. Among them, toxic shock syndrome (TSS) is a prototypic acute intoxication caused by the pyrogenic exotoxin family of superantigens. In this study, we investigated the pathophysiological mechanism of TSS using the Yersinia pseudotuberculosis-derived mitogen (YPM) and its point mutants. The results indicated that YPM could induce toxic shock in BALB/c mice but not in T cell-deficient SCID mice. We found that Vbeta8(+) T cells activated by YPM migrated from peripheral blood to liver as early as 1 h after injection of YPM and that serum level of IFN-gamma was significantly elevated 4 h after YPM injection. Co-administration of anti-IFN-gamma antibody or anti-YPM monoclonal antibody alleviated the liver injury and protected mice from YPM-induced death. Moreover, anti-YPM antibody also suppressed the early migration of Vbeta8(+) T cells from the peripheral circulation and the elevation of serum IFN-gamma level, indicating a pivotal role of T cells in inducing shock in our mouse model.

DNA adenine methylase overproduction in Yersinia pseudotuberculosis alters YopE expression and secretion and host immune responses to infection

Yersinia pseudotuberculosis mutants that overproduce the DNA adenine methylase (Dam) are highly attenuated, confer fully protective immune responses, and secrete several Yersinia virulence proteins (Yersinia outer proteins [Yops]) under conditions that are nonpermissive for secretion in wild-type strains. We examined here the effects of Dam overproduction on Yersinia virulence determinant expression and secretion, as well as the host immune response to Yersinia antigens. Western blot analysis with convalescent antisera identified several low-calcium-responsive antigens whose synthesis was affected by Dam overproduction. One of these antigens was shown to be the type III secretion effector protein, YopE, a cytotoxin involved in antiphagocytosis. Dam overproduction disrupted both the thermal and calcium regulation of YopE synthesis and relaxed the thermal but not the calcium dependence of YopE secretion. Altered expression and/or secretion of Yersinia proteins in Dam-overproducing strains may contribute to the decreased virulence and heightened immunity observed in vaccinated hosts and may provide a means by which to deliver heterologous antigens and/or immune modulators of the inflammatory response.

Superantigen YPMa exacerbates the virulence of Yersinia pseudotuberculosis in mice

Yersinia pseudotuberculosis, a gram-negative bacterium responsible for enteric and systemic infection in humans, produces a superantigenic toxin designated YPMa (Y. pseudotuberculosis-derived mitogen). To assess the role of YPMa in the pathogenesis of Y. pseudotuberculosis, we constructed a superantigen-deficient mutant and compared its virulence in a mouse model of infection to the virulence of the wild-type strain. Determination of the survival rate after intravenous (i.v.) bacterial inoculation of OF1 mice clearly showed that inactivation of ypmA, encoding YPMa, reduced the virulence of Y. pseudotuberculosis. Mice infected i.v. with 10(4) and 10(5) wild-type bacteria died within 9 days, whereas mice infected with the ypmA mutant survived 12 and 3 days longer, respectively. This decreased virulence of the ypmA mutant strain was not due to an impaired colonization of the spleen, liver, or lungs. In contrast to i.v. challenge, bacterial inoculation by the intragastric (i.g.) route did not reveal any difference in virulence between wild-type Y. pseudotuberculosis and the ypmA mutant since the 50% lethal doses were identical for both strains. Moreover, inactivation of ypmA gene did not affect the bacterial growth of Y. pseudotuberculosis in Peyer's patches, mesenteric lymph nodes (MLNs), and spleen after oral infection. Histological studies of spleen, liver, lungs, heart, Peyer's patches, and MLNs after i.v. or i.g. challenge with the wild type or the ypmA mutant did not reveal any feature that can be specifically related to YPMa. Our data show that the superantigenic toxin YPMa contributes to the virulence of Y. pseudotuberculosis in systemic infection in mice.

Yersinia enterocolitica and Yersinia pseudotuberculosis

Yersinia enterocolitica can cause enteritis, right lower-quadrant pain mimicking appendicitis, reactive arthritis, and erythema nodosum. This organism is transmitted through food, animal contact, and contaminated blood products. Patients with iron excess are at a higher risk for serious infection. This article describes the history, microbiology, virulence factors, epidemiology, clinical manifestations, diagnosis, and therapy of Y. enterocolitica and Y. pseudotuberculosis. In addition, the immune response of those developing reactive arthritis following infection with Y. enterocolitica is discussed.

An outbreak of foal yersiniosis in Poland: pathological and bacteriological examination

In the springtime of 1995, 10 per cent of foals at a stud-farm died due to suppurative lesions. Three dead foals were examined. The manifestations of watery diarrhoea and pneumonia were observed. A profuse growth of an enterotoxigenic strain of Yersinia pseudotuberculosis was obtained from the internal organs of the foals. The foals with clinical symptoms of pneumonia and watery diarrhoea were immunized with Propionibacterium acnes t. II. All mares and their offspring from the stud were treated with an immunomodulator (Propionibacterium acnes t. II) and then vaccinated with a formalin-inactivated culture of Yersinia pseudotuberculosis.

Acute renal failure associated with Yersinia pseudotuberculosis infection in children

We report 45 pediatric cases of Yersinia pseudotuberculosis infection confirmed by stool culture between May 1993 and June 1994. In 41 (91.1%) cases there had been contact with untreated well or mountain water. Y. pseudotuberculosis was also isolated from 4 samples of mountain spring water thought to be the sources of infection. During the course of the illness, acute renal failure (ARF) developed in 6 patients (13.6%). The age distribution of the ARF group (12.3 +/- 1.2 years) was significantly different from the non-ARF group (8.0 +/- 3.2 years). The serogroups of Y. pseudotuberculosis isolates from stool samples were 5 (n = 30) and 4 (n = 15). Isolates from the water samples were all serogroup 5. The main symptoms of both groups were fever, rash, abdominal pain, and vomiting. ARF developed between the 2nd and 14th days (mean 6 days) after the onset of fever, and oliguria (< 400 ml/m2 per day) developed in 3 patients (3/6, 50%) immediately after their fevers had subsided. ARF underwent a benign course, with complete recovery within a maximum of 4 weeks (mean 10.2 days), with 1 exceptional patient requiring hemodialysis. Renal biopsy showed evidence of tubulointerstitial nephritis. Y. pseudotuberculosis should be included as one of the causes of acute interstitial nephritis causing ARF in children, especially when the children have histories of drinking untreated water in endemic areas.

[Masshoff's disease]

Masshoff's disease (pseudotuberculous mesadenitis) was diagnosed in a 20-year-old male on the basis of histological investigation of surgically removed appendix and ileocaecal lymph nodes. The appendix was intact. Hyperplasia of lymphoid tissue with formation of small abscesses and karyorrhexis of neutrophils, but without giant polynuclear cells was histologically revealed in lymph nodes. Foci of fibrinoid necrosis were found in lymph node capsules. Serological test for pseudotuberculosis was strongly positive ( +).

Outbreaks of yersiniosis caused by Yersinia pseudotuberculosis in farmed cervids

Yersiniosis, caused by Yersinia pseudotuberculosis, was diagnosed in 25 deer submitted to the Veterinary Diagnostic Laboratories of the Ontario Ministry of Agriculture and Food from 8 farms in Ontario, Canada, over the 4-year period of January 1990 to December 1993. The organism was cultured, usually in large numbers, from the intestines and, less frequently, mesenteric lymph nodes and/or the spleen of 13 red deer (Cervus elaphus), 6 elk (C. e. canadiensis), 4 fallow deer (Dama dama), and 2 red deer-elk hybrids. Outbreaks occurred almost exclusively in the fall (September-November) and affected recently weaned calves, 4-6 months old. Sudden death usually signalled the start of an outbreak. Outbreaks often occurred during inclement weather; usually a sudden cold snap, with or without rain, after a period of relatively mild fall weather. At necropsy, the animals were usually emaciated and dehydrated, and the perineum and tail were sometimes fecally stained. The small and large intestines were congested and filled with serofibrinous and/or seroanguineous fluid. Mesenteric lymph nodes were edematous and congested. Microabscesses surrounding large bacterial colonies in the lamina propria in the jejunum and ileum were typical lesions seen histologically. Peyer's patches were depleted and sometimes contained microabscesses. Purulent lymphadenitis associated with bacterial colonies was the prominent histologic lesion in mesenteric lymph nodes.

Pathogenicity of a strain of Yersinia pseudotuberculosis isolated from a pig with porcine colitis syndrome

A strain of Yersinia pseudotuberculosis (NCTC 12718), isolated from a seven-week-old pig suffering from an ulcerative typhlocolitis, was inoculated orally into 16 growing pigs in two separate experiments. At necropsy 10 days later, typhlocolitis was present in nine of the pigs, and it was accompanied by diarrhoea in four cases. In both the original case and in the experimental pigs, the typhlocolitis was characterised by microabscesses of the lamina propria, frequently involving ulceration or erosion of the surface epithelium. The organism was of serotype IIa, which has not been isolated previously from pigs in the United Kingdom. Y pseudotuberculosis may be the aetiological agent responsible in some cases of porcine colitis syndrome.

[The protective activity of Yersinia pseudotuberculosis antigens]

Samples of Y.pseudotuberculosis (serovar I) antigens, represent a high-molecular lipopolysaccharide (LPS) fraction with a mol. wt. of 22.5 kD and fractions of outer membrane proteins isolated by the method of M. Osborn and R. Munson (1974), were tested in comparison with the activity with live cells of Y. pseudotuberculosis I attenuated mutant KV 9/2, having lost its Cad plasmid of virulence with a mol. wt. of 47 MD and carrying 2 attenuating markers: resistance to crystal violet and nalidixic acid. In experiments on guinea pigs pathomorphological studies demonstrated high protective activity of Y.pseudotuberculosis I attenuated mutant KV 9/2 and a pronounced protective effect achieved after the immunization of the animals with complex biopolymers, including a high-molecular LPS fraction and outer membrane proteins.

[Morphology of granulomatous inflammation in pseudotuberculosis]

The study of pathology in pseudotuberculosis has showed that clinical and morphological nature of the disease is related to granulomatous inflammation in organs and tissues. The authors have established that a relapsing course of this infection may be due to pronounced specific sensitization of the body when granulomas appear in large numbers. Morphogenesis of acute granulomatous inflammation in pseudotuberculosis reflects a consecutive involvement of cellular reactions of the immediate and delayed hypersensitivity. In the authors' opinion pseudotuberculosis granulomas may be assigned to immune hypersensitive granulomas of mixed type according to the classification suggested by A. I. Strukov and O. Ya. Kaufman. The data obtained allow a hypothesis that granulomas tending to cause a purulent liquefaction and necrosis, like pseudo-tuberculous granulomas, could be considered as a morphological sign of granulocytic-macrophagal immune deficiency.

Epizootic of Yersinia pseudotuberculosis in a wildlife park

An epizootic attributable to Yersinia pseudotuberculosis infection was confirmed in captive ruminants in a wildlife park by microbiologic and histologic findings. An epornitic of Y pseudotuberculosis infection was identified at the same period in a vicinity near the ruminant deaths. Yersinia pseudotuberculosis can infect human beings and cause acute enteritis and mesenteric lymphadenitis. People in contact with infected animals should use extreme caution and use good sanitary precautions to preclude transmission of this agent.

A spontaneous Yersinia pseudotuberculosis-infection in a monkey-colony

A spontaneous Yersinia pseudotuberculosis (Y.p.) infection in one African Green Monkey (Cercopithecus aethiops), and nine Squirrel Monkeys (Saimiri sciureus), is reported. The clinical findings, laboratory results and pathological findings are presented. The digestive system was the most affected organ in the acute phase of the Y.p. infection, while in the subacute and chronic phases, the alterations of the lymphatic tissues, spleen or liver were severe.

Acute mesenteric lymphadenitis due to Yersinia pseudotuberculosis lacking a virulence plasmid

A serotype 4a strain of Yersinia pseudotuberculosis lacking the virulence plasmid pYV (pYV- strain) was isolated from the mesenteric lymph nodes but not from the stool or the appendix of a 10-year-old girl with a diagnosis of acute mesenteric lymphadenitis. Microscopically, reticulocytic abscess and lymphadenitis were persent in the enlarged mesenteric lymph nodes. Antibody against the isolate was detected in the serum. The isolate was negative for the presence of plasmid pYV and plasmid pYV-mediated properties, including autoagglutination and calcium dependency, but was positive for chromosome-mediated properties, including invasion into HeLa cells and tissues of mice and the Serény test. Mice were orally infected with this pYV- strain, and rapid elimination from the intestine occurred 14 days later. Hence, the potential to inhibit the phagocytosis encoded by plasmid pYV was lacking. As the pYV- strain was recovered from the mesenteric lymph nodes and the spleen, the invasiveness was encoded by chromosomal genes. The count of the pYV- strain in the mesenteric lymph nodes increased to 10(4.6) cells per g within 4 days. These findings suggest that pYV- Y. pseudotuberculosis was the causative agent of acute mesenteric lymphadenitis in the absence of gastroenteritis.

Acute tubulointerstitial nephritis associated with Yersinia pseudotuberculosis infection

Two siblings infected with Yersinia pseudotuberculosis suffered from acute renal failure about 2 weeks after the onset of the disease. Renal histology in both siblings showed acute tubulointerstitial nephritis. Yersinia pseudotuberculosis type VB was isolated from feces of one of them, antibodies to Yersinia pseudotuberculosis type VB in their sera were elevated. The results of the present study suggest that acute renal failure complicating infections with Yersinia pseudotuberculosis is due to acute tubulointerstitial nephritis.

Yersinia species isolated from sheep with enterocolitis

In 40 submissions to the Regional Veterinary Laboratory (RVL) Wagga Wagga from sheep in southern New South Wales from 1981 to 1989, 53 isolates of Yersinia sp were recovered from 45 sheep in 37 flocks. Of 53 isolates, 26 were identified as Y. pseudotuberculosis, 20 as Y. enterocolitica, 5 as Y. intermedia and 2 as Y. frederiksenii. Twelve isolates of Y. pseudotuberculosis tested in the slide agglutination test all belonged to serotype III. The 20 Y. enterocolitica isolates were categorised biochemically as biotype 5 strains and, of 6 isolates serotyped, all belonged to serogroup 2,3. Outbreaks of yersiniosis were most common in late winter and early spring and affected flocks often had experienced a change in husbandry. Infection with Yersinia sp was associated with diarrhoea, illthrift and mortality. At necropsy, congestion and occasionally thickening of the intestinal mucosa were observed in affected sheep. Gastrointestinal nematodiasis and coccidiosis often were concurrent findings. The characteristic histological lesion in sheep infected with Y. pseudotuberculosis was acute segmental suppurative erosive enterocolitis. There were no lesions consistently associated with Y. enterocolitica, Y. intermedia or Y. frederiksenii.

[Yersinia pseudotuberculosis in New World monkeys]

It is reported on four cases of pseudotuberculosis in 2 Saimiri sciureus, 1 Callithrix jacchus/penicillata hybrid and 1 S. oedipus. The animals came from two different groups, one being infected with Y. pseudotuberculosis serotype I, the other with Y. pseudotuberculosis serotype II. All cases showed intestinal infection of thermophile Campylobacter. Remarkable were severe haemorrhagic components and the distinct RHS-proliferation, especially in the mesenteric lymphatic nodes.

[The biological action of Yersinia pseudotuberculosis endotoxin]

Experimental studies on guinea pigs have shown that Y. pseudotuberculosis lipopolysaccharide is capable of inducing endotoxinemia accompanied by the development of the thrombohemorrhagic syndrome. In cases of pseudotuberculosis the importance of the increased synthesis of prostaglandins and cyclic nucleotides with the prevalence of PGF2 alpha and cGMP in the genesis of toxico-allergic manifestations of pathologic processes has been established. The pathomorphological picture of pseudotuberculosis endotoxinemia is characterized by sludge, the vascular thrombosis of the microcirculatory bed, diapedetic hemorrhages, delymphatization of the immunogenetic organs. The moderately pronounced action of indomethacin, a prostaglandin inhibitor, on the manifestations of pseudotuberculosis endotoxinemia has been revealed.

The cytotoxic protein YopE of Yersinia obstructs the primary host defence

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

Yersinia pseudotuberculosis enteritis in four calves

A Yersinia pseudotuberculosis enteritis in four yearling calves is described. This is the first report of this organism causing enteric disease in domestic cattle in North America.

Enteritis in cattle due to Yersinia pseudotuberculosis infection

A selective medium was used to isolate Yersinia sp from the intestinal tract of 222 scouring cattle in Gippsland during 1985 and 1986. Intestinal infection with Y. pseudotuberculosis, particularly of serotype III, was found to be especially prevalent in weaned calves, yearlings and young adult cattle. Clinically affected cattle had a profuse liquid diarrhoea and many were systemically ill. Haematological changes suggestive of infection were present in 38 of 49 of these cattle. At least 35 cattle died and characteristic microabscesses were demonstrated in the intestinal mucosa of 20 of 26 examined histologically. Y. pseudotuberculosis was sensitive to tetracyclines in vitro and this drug produced a rapid bacteriological cure. Yersiniosis occurred during the winter, spring and early summer. Challenge of adult cattle with Y. pseudotuberculosis serotype III did not result in intestinal colonisation or clinical disease. Intestinal infection was, however, established in 4 weaned calves and haematological changes and antibody production were demonstrated in them. Intestinal microabscesses were seen in three calves killed on days 8, 14 and 18 after challenge. The fourth calf eliminated infection by day 18 and no lesions were demonstrated when it was killed on day 72. There is a very high prevalence of antibodies reacting with Y. pseudotuberculosis serotype III in adult cattle. It is concluded that cattle are a common host for this bacterium, infection being frequent, with clinical and fatal disease occurring occasionally. The factors leading to clinical disease are unknown.

Yersinia pseudotuberculosis sepsis presenting as multiple liver abscesses

A 50-year-old man with diabetes was found to have sepsis with multiple small hepatic abscesses secondary to Yersinia pseudotuberculosis which were detected by computed tomography (CT) scan. Sepsis with Y. pseudotuberculosis is uncommon but usually seen in patients with underlying liver disease. Those patients with liver abscesses invariably have multiple small abscesses. Widespread use of CT scanning is likely to uncover more cases of hepatic microabscesses; in the appropriate clinical setting, Y. pseudotuberculosis should be considered as a possible cause.

Enterocolitis in cattle associated with Yersinia pseudotuberculosis infection

A syndrome in cattle of diarrhoea and death associated with enteric Yersinia pseudotuberculosis infection is described. Outbreaks occurred during winter and early spring in adult cattle grazing pastures waterlogged by recent flooding or persistent heavy rain. Antibiotic therapy was effective early in the course of the syndrome. At necropsy there was severe acute enterocolitis, and bacteria consistent with Y. pseudotuberculosis were observed in the lesions. This organism could usually be isolated from the intestines of affected animals but was recovered less often from other organs. Representative isolates were identified as Y. pseudotuberculosis serotype III. The association of this syndrome with waterlogged pastures and low temperatures suggests that these conditions favour transmission of Y. pseudotuberculosis infection in cattle. The role of Y. pseudotuberculosis as primary pathogen requires confirmation.

[Structural changes in the kidneys during experimental infection caused by Yersinia pseudotuberculosis]

A pronounced affinity of Yersinia pseudotuberculosis to the epithelium of renal tubules has been first stated. Microorganisms disseminate through blood into the renal tissue and enter the winding tubule lumen as part of glomerular filtrate. Due to invasion and intensive multiplication of Yersinia pseudotuberculosis within epitheliocytes the epithelium is damaged and necrotic nephrosis develops. Intensive microbial colonization was noted in the tubule lumen. Extra-capillary glomerulonephritis due to Yersinia pseudotuberculosis was detected for the first time. Our data can account for long-term renal disorders in patients with pseudotuberculosis.

[Interaction of Yersinia pseudotuberculosis with the epithelium of the small intestine in experimental infection]

Some data showing specific ways of interaction of Yersinia pseudotuberculosis with the epithelium of the small intestinal mucosa have been received for the first time by using light microscopy of semithin sections. Comparative study of the lesion of the epithelium of different parts of rabbit small intestine by oral inoculation with Yersinia tuberculosis has expanded the ideas of the infection entry. It has been established for the first time that the most intensive penetration of the microorganisms into the epithelium of the mucous membrane takes place in the duodenum and jejunum. As the infected contents is evacuated via the intestinal tract, the Yersinia pathogenicity decreases, and in the ileum, the invasion of the microorganisms becomes less pronounced. It has been revealed that in pseudotuberculosis, there takes place a repeated dissemination of the infection in the intestinal tract because of decay of the involved enterocytes, which is of pathogenetic importance for the progress and outcome of the infection.

[Invasiveness characteristics of the causative agent of pseudotuberculosis]

The comparative characteristics of the invasiveness of Y. pseudotuberculosis, the most important element of its pathogenicity, is given on the basis of the results obtained in testing 57 Y. pseudotuberculosis strains and 23 Y. enterocolitica strains, all of them recently isolated, on experimental models (the monolayer cultures of Hep-2 cells, the enteral inoculation of mice and guinea pigs, the keratoconjunctival test). The invasiveness of Y. pseudotuberculosis has been shown to be manifested immediately after the ir adhesion and accompanied by the multiplication of these microbes in the cytoplasma of Hep-2 cells and, in animal experiments, in the cytoplasma of the epithelial cells of mucous membranes and the macrophages of lamina propria mucosae. The intracellular multiplication leads to the destruction of the layer of Hep-2 cells and, in animal experiments, to the disintegration of the infected cells, the development of Hep-2 cells and, in animal experiments, to the disintegration of the infected cells, the development of erosions and ulcers, purulent lymphadenitis of the regional lymph nodes, generalized infection with multiple abscesses in internal organs. Y. enterocolitica strains under investigation induced neither conjunctivitis, nor enterocolitis in the animals, and in experiments on Hep-2 cells, these strains, having less pronounced adhesive properties, either showed sharply limited adhesiveness without the capacity for intracellular multiplication and cytotoxicity, or proved to be absolutely noninvasive.