Cytotoxic necrotizing factor-Y boosts Yersinia effector translocation by activating Rac protein

Pathogenic Yersinia spp. translocate the effectors YopT, YopE, and YopO/YpkA into target cells to inactivate Rho family GTP-binding proteins and block immune responses. Some Yersinia spp. also secrete the Rho protein activator cytotoxic necrotizing factor-Y (CNF-Y), but it has been unclear how the bacteria may benefit from Rho protein activation. We show here that CNF-Y increases Yop translocation in Yersinia enterocolitica-infected cells up to 5-fold. CNF-Y strongly activated RhoA and also delayed in time Rac1 and Cdc42, but when individually expressed, constitutively active mutants of Rac1, but not of RhoA, increased Yop translocation. Consistently, knock-out or knockdown of Rac1 but not of RhoA, -B, or -C inhibited Yersinia effector translocation in CNF-Y-treated and control cells. Activation or knockdown of Cdc42 also affected Yop translocation but much less efficiently than Rac. The increase in Yop translocation induced by CNF-Y was essentially independent of the presence of YopE, YopT, or YopO in the infecting Yersinia strain, indicating that none of the Yops reported to inhibit translocation could reverse the CNF-Y effect. In summary, the CNF-Y activity of Yersinia strongly enhances Yop translocation through activation of Rac.

Gut proteases target Yersinia invasin in vivo

BACKGROUND

Yersinia enterocolitica is a common cause of food borne gastrointestinal disease. After oral uptake, yersiniae invade Peyer's patches of the distal ileum. This is accomplished by the binding of the Yersinia invasin to β1 integrins on the apical surface of M cells which overlie follicle associated lymphoid tissue. The gut represents a barrier that severely limits yersiniae from reaching deeper tissues such as Peyer's patches. We wondered if gut protease attack on invasion factors could contribute to the low number of yersiniae invading Peyer's patches.

FINDINGS

Here we show that invasin is rapidly degraded in vivo by gut proteases in the mouse infection model. In vivo proteolytic degradation is due to proteolysis by several gut proteases such as trypsin, α-chymotrypsin, pancreatic elastase, and pepsin. Protease treated yersiniae are shown to be less invasive in a cell culture model. YadA, another surface adhesin is cleaved by similar concentrations of gut proteases but Myf was not cleaved, showing that not all surface proteins are equally susceptible to degradation by gut proteases.

CONCLUSIONS

We demonstrate that gut proteases target important Yersinia virulence factors such as invasin and YadA in vivo. Since invasin is completely degraded within 2-3 h after reaching the small intestine of mice, it is no longer available to mediate invasion of Peyer's patches.

A key role for E-cadherin in intestinal homeostasis and Paneth cell maturation

Background

E-cadherin is a major component of adherens junctions. Impaired expression of E-cadherin in the small intestine and colon has been linked to a disturbed intestinal homeostasis and barrier function. Down-regulation of E-cadherin is associated with the pathogenesis of infections with enteropathogenic bacteria and Crohn's disease.

Methods and Findings

To genetically clarify the function of E-cadherin in intestinal homeostasis and maintenance of the epithelial defense line, the Cdh1 gene was conditionally inactivated in the mouse intestinal epithelium. Inactivation of the Cdh1 gene in the small intestine and colon resulted in bloody diarrhea associated with enhanced apoptosis and cell shedding, causing life-threatening disease within 6 days. Loss of E-cadherin led cells migrate faster along the crypt-villus axis and perturbed cellular differentiation. Maturation and positioning of goblet cells and Paneth cells, the main cell lineage of the intestinal innate immune system, was severely disturbed. The expression of anti-bacterial cryptidins was reduced and mice showed a deficiency in clearing enteropathogenic bacteria from the intestinal lumen.

Conclusion

These results highlight the central function of E-cadherin in the maintenance of two components of the intestinal epithelial defense: E-cadherin is required for the proper function of the intestinal epithelial lining by providing mechanical integrity and is a prerequisite for the proper maturation of Paneth and goblet cells.

In vivo analysis of Yersinia enterocolitica infection using luxCDABE

Yersiniae expressing an L-arabinose-inducible luxCDABE reporter were used to analyze the colonization of mice. Infection of live mice was followed over a period of 6 days. These experiments revealed frequent colonization of cervical lymph nodes after oral, but not intravenous infection. Furthermore, the well-known colonization of the small intestine, Peyer's patches (PPs) of the ileum, the cecal lymph follicle, mesenteric lymph nodes, liver, and spleen was easily detectable. Removal of the intestinal tract of mice revealed that the number of abscessed PPs and other tissues can be easily quantified. Experiments with an invasin mutant expressing luxCDABE revealed a significantly reduced number of abscessed PPs, cecal lymph follicles, and lymph nodes in yersiniae lacking invasin.

Analysis of Yersinia enterocolitica invasin expression in vitro and in vivo using a novel luxCDABE reporter system

A novel luxCDABE plasmid for the analysis of promoter elements by site-specific integration into the genome of Yersinia enterocolitica was constructed. The versatility of this reporter system was demonstrated by comparing the activity of the inv promoter in the Y. enterocolitica high-pathogenic serotype O : 8 (strain WA-314) with that of the low pathogenic serotype O : 9 (strain Y127). The luciferase activity of a transcriptional fusion between the inv promoter of serotype O : 8 and luxCDABE was about fourfold lower than the activity of the respective O : 9 promoter. This correlated with lower invasin production by Y. enterocolitica serotype O : 8 compared with serotypes O : 9, O : 3 and O : 5,27. However, Y. enterocolitica of serotype O : 8 revealed higher invasiveness than serotype O : 9. When both invasins were expressed in trans at similar levels in the Y. enterocolitica O : 8 Δinv background strain, cell invasion assays showed a slightly higher invasiveness of the strain producing Inv(O : 8) than the strain producing Inv(O : 9). We provide experimental evidence that this might be due to a higher binding capacity of Inv(O : 8) for cells expressing β1 integrins compared with Inv(O:9). The Y. enterocolitica O : 8 strain harbouring the P inv (O : 8) : : luxCDABE fusion was then successfully used to follow inv expression in a mouse infection model. These experiments showed for the first time that the inv promoter is active in infected living mice, especially in Peyer's patches of the ileum, the caecal lymph follicle, and the lymph nodes, liver and spleen. The production of invasin in the spleen was demonstrated by Western blot analysis. In conclusion, the presented reporter system enables stable genomic integration of the luxCDABE operon into the chromosome of Yersinia, facilitates in vitro quantification of promoter activities under different bacterial growth conditions, and enables detection of promoter activities in a mouse model.

Beta1 integrin-dependent engulfment of Yersinia enterocolitica by macrophages is coupled to the activation of autophagy and suppressed by type III protein secretion

Autophagy is a central lysosomal degradation process that is essential for the maintenance of cellular homeostasis. Autophagy has furthermore emerged as integral part of the host immune response. Autophagic processes promote the separation and degradation of intracellular microorganisms which contributes to the development of innate and adaptive immunity. Some pathogenic microbes have therefore evolved mechanisms to evade or impede autophagy. We analyzed the effects of the enteropathogenic bacterium Yersinia enterocolitica on autophagy in macrophages. Yersiniae use a number of defined adhesins and secreted proteins to manipulate host immune responses. Our results showed that Y. enterocolitica defective in type III protein secretion efficiently activated autophagy in macrophages. Autophagy was mediated by the Yersinia adhesins invasin and YadA and particularly depended on the engagement of beta(1) integrin receptors. Several autophagy-related events followed beta(1) integrin-mediated engulfment of the bacteria including the formation of autophagosomes, processing of the marker protein LC3, redistribution of GFP-LC3 to bacteria-containing vacuoles, and the segregation of intracellular bacteria by autophagosomal compartments. These results provide direct evidence for the linkage of beta(1) integrin-mediated phagocytosis and autophagy induction. Multiple microbes signal through integrin receptors, and our results suggest a general principle by which the sensing of an extracellular microbe triggers autophagy. Owing to the importance of autophagy as host defense response, wild-type Y. enterocolitica suppressed autophagy by mobilizing type III protein secretion. The subversion of autophagy may be part of the Y. enterocolitica virulence strategy that supports bacterial survival when beta(1) integrin-dependent internalization and autophagy activation by macrophages are deleterious for the pathogen.

Yersinia enterocolitica Yop mutants as oral live carrier vaccines

Attenuated enteropathogenic yersiniae that translocate heterologous antigens into the cytosol of antigen presenting cells via their type three secretion system (TTSS) are considered promising candidates for the development of live oral vaccine carrier strains that induce CD8 T cell responses. Wild type Yersinia enterocolitica of serotype O:8 however efficiently suppresses the immune response of the host by translocating effector proteins called Yersinia outer proteins (Yops) into the cytosol of immune cells. We therefore tested immunogenicity, protective efficacy, and virulence ofyop mutants that translocate the model antigen Listeriolysin (LLO) of Listeria monocytogenes in a mouse model. A deltayopP mutant-based vaccine carrier strain induced the highest numbers of LLO91-99-specific CD8 T cells and effectively protected mice against a lethal challenge with Listeria whereas deltayopPT, deltayopPV(K42Q), and deltayopPO mutants of Y. enterocolitica induced fewer CD8 T cells and conferred only partial protection. The deltayopPH, deltayopPE, deltayopPM, and deltayopPQ mutants induced the weakest CD8 T cell response and did not significantly protect mice against Listeria presumably due to the strong attenuation of these strains in the mouse model. Even though a Y. enterocolitica strain WA-C(pTTSS), which translocated only LLO (but not Yops), induced superior MHC class I-restricted antigen presentation in DC compared to the deltayopP mutants in vitro, this strain was not able to significantly colonize mouse tissue or to induce CD8 T cell responses in vivo. The success in designing a Yersinia oral vaccine carrier is therefore dependent to a great extent on the subtle balance between immunogenicity and attenuation.

Cross-talk between type three secretion system and metabolism in Yersinia

Pathogenic yersiniae utilize a type three secretion system (T3SS) to inject Yop proteins into host cells in order to undermine their immune response. YscM1 and YscM2 proteins have been reported to be functionally equivalent regulators of the T3SS in Yersinia enterocolitica. Here, we show by affinity purification, native gel electrophoresis and small angle x-ray scattering that both YscM1 and YscM2 bind to phosphoenolpyruvate carboxylase (PEPC) of Y. enterocolitica. Under in vitro conditions, YscM1, but not YscM2, was found to inhibit PEPC with an apparent IC(50) of 4 mum (K(i) = 1 mum). To analyze the functional roles of PEPC, YscM1, and YscM2 in Yop-producing bacteria, cultures of Y. enterocolitica wild type and mutants defective in the formation of PEPC, YscM1, or YscM2, respectively, were grown under low calcium conditions in the presence of [U-(13)C(6)]glucose. The isotope compositions of secreted Yop proteins and nine amino acids from cellular proteins were analyzed by mass spectrometry. The data indicate that a considerable fraction of oxaloacetate used as precursor for amino acids was derived from [(13)C(3)]phosphoenolpyruvate by the catalytic action of PEPC in the wild-type strain but not in the PEPC(-) mutant. The data imply that PEPC is critically involved in replenishing the oxaloacetate pool in the citrate cycle under virulence conditions. In the YscM1(-) and YscM2(-) mutants, increased rates of pyruvate formation via glycolysis or the Entner-Doudoroff pathway, of oxaloacetate formation via the citrate cycle, and of amino acid biosynthesis suggest that both regulators trigger the central metabolism of Y. enterocolitica. We propose a "load-and-shoot cycle" model to account for the cross-talk between T3SS and metabolism in pathogenic yersiniae.

Salmonella type III-mediated heterologous antigen delivery: A versatile oral vaccination strategy to induce cellular immunity against infectious agents and tumors

Salmonella type III secretion system (T3SS)-mediated translocation can be used for efficient delivery of heterologous antigens to the cytosol of antigen-presenting cells leading to prominent CD8 T-cell priming in orally immunized mice. The time point and duration of hybrid protein translocation during the Salmonella infection cycle can be modulated by employing various type III carrier molecules. The p60 protein of Listeria monocytogenes was used as model antigen to construct chimeric SspH2/p60. SspH2 is a "Salmonella pathogenicity island 2" (SPI2) protein that is known to be translocated by Salmonella during intracellular survival and replication in macrophages. This SPI2 carrier molecule is sufficient to induce a concomitant p60-specific CD4 and CD8 T-cell response in Salmonella-vaccinated mice. Moreover, T3SS-mediated antigen delivery results in an efficient priming of central and effector memory CD8 T cells in spleens of these animals. This vaccination strategy can also be employed to efficiently protect mice from an aggressive fibrosarcoma transfected with p60 in a prophylactic setting.

Yersinia as oral live carrier vaccine: influence of Yersinia outer proteins (Yops) on the T-cell response

Attenuated enteropathogenic Yersinia strains are attractive candidates for the development of oral live carrier vaccines. Yersiniae colonize the small intestine and invade lymphoid tissue of the terminal ileum where they replicate extracellularly. Yersiniae can be engineered to secrete or translocate heterologous antigens into the cytosol of antigen-presenting cells by their type 3 secretion system (T3SS). This results in the induction of both cellular and humoral immune responses to heterologous antigens of viral, bacterial and parasitic origin. In this review, we summarize the progress in developing Yersinia-based vaccine carrier strains by mutating the T3SS effector proteins of Yersinia called Yops (Yersinia outer proteins) to both attenuate the strains and to modulate the T-cell response.

Yersinia enterocolitica infection of mice reveals clonal invasion and abscess formation

Yersinia enterocolitica is a common cause of food-borne gastrointestinal disease leading to self-limiting diarrhea and mesenteric lymphadenitis. Occasionally, focal abscess formation in the livers and spleens of certain predisposed patients (those with iron overload states such as hemochromatosis) is observed. In the mouse oral infection model, yersiniae produce a similar disease involving the replication of yersiniae in the small intestine, the invasion of Peyer's patches, and dissemination to the liver and spleen. In these tissues and organs, yersiniae are known to replicate predominantly extracellularly and to form microcolonies. By infecting mice orally with a mixture of equal amounts of green- and red-fluorescing yersiniae (yersiniae expressing green or red fluorescent protein), we were able to show for the first time that yersiniae produce exclusively monoclonal microcolonies in Peyer's patches, the liver, and the spleen, indicating that a single bacterium is sufficient to induce microcolony and microabscess formation in vivo. Furthermore, we present evidence for the clonal invasion of Peyer's patches from the small intestine. The finding that only very few yersiniae are required to establish microcolonies in Peyer's patches is due to both Yersinia-specific and host-specific factors. We demonstrate that yersiniae growing in the small intestinal lumen show strongly reduced levels of invasin, the most important factor for the early invasion of Peyer's patches. Furthermore, we show that the host severely restricts sequential microcolony formation in previously infected Peyer's patches.

Serogroup-related escape of Yersinia enterocolitica YopE from degradation by the ubiquitin-proteasome pathway

Pathogenic Yersinia spp. employ a type III protein secretion system that translocates several Yersinia outer proteins (Yops) into the host cell to modify the host immune response. One strategy of the infected host cell to resist the bacterial attack is degradation and inactivation of injected bacterial virulence proteins through the ubiquitin-proteasome pathway. The cytotoxin YopE is a known target protein of this major proteolytic system in eukaryotic cells. Here, we investigated the sensitivity of YopE belonging to different enteropathogenic Yersinia enterocolitica serogroups to ubiquitination and proteasomal degradation. Analysis of the YopE protein levels in proteasome inhibitor-treated versus untreated cells revealed that YopE from the highly pathogenic Y. enterocolitica serotype O8 was subjected to proteasomal destabilization, whereas the YopE isotypes from serogroups O3 and O9 evaded degradation. Accumulation of YopE from serotypes O3 and O9 was accompanied by an enhanced cytotoxic effect. Using Yersinia strains that specifically produced YopE from either Y. enterocolitica O8 or O9, we found that only the YopE protein from serogroup O8 was modified by polyubiquitination, although both YopE isotypes were highly homologous. We determined two unique N-terminal lysines (K62 and K75) in serogroup O8 YopE, not present in serogroup O9 YopE, that served as polyubiquitin acceptor sites. Insertion of either lysine in serotype O9 YopE enabled its ubiquitination and destabilization. These results define a serotype-dependent difference in the stability and activity of the Yersinia effector protein YopE that could influence Y. enterocolitica pathogenesis.

Staphylococcus pettenkoferi sp. nov., a novel coagulase-negative staphylococcal species isolated from human clinical specimens

Five coagulase-negative, novobiocin-susceptible staphylococcal strains were isolated from human blood cultures in different German and Belgian medical facilities. A novel species, ‘Staphylococcus pettenkoferi’ was proposed recently to accommodate two of these strains (B3117T and A6664), although the name was not validly published. All five strains belonged to the genus Staphylococcus because they were non-motile, Gram-positive, catalase-positive cocci with peptidoglycan type (A3α type l-lys–gly2–4–l-Ser–Gly), menaquinone pattern (MK-7, MK-6 and MK-8) and major cellular fatty acids (ai-C15 : 0, ai-C17 : 0 and i-C15 : 0) that corresponded to those of staphylococci. Phenotypically, the isolates most closely resembled Staphylococcus capitis subsp. capitis and Staphylococcus auricularis, but they could be distinguished from these species by physiological tests and chemotaxonomic investigations. The results of DNA–DNA hybridization, chemotaxonomic investigations and 16S rRNA gene and RNA polymerase B gene (rpoB) sequence analysis enabled strains B3117T, K6999, 229 and 230 to be differentiated genotypically and phenotypically from known Staphylococcus species, indicating that these isolates are representatives of a novel species. The name Staphylococcus pettenkoferi sp. nov. is proposed for this novel species, with strain B3117T (=CIP 107711T=CCUG 51270T) as the type strain. Due to differences in the results of physiological and chemotaxonomic investigations and DNA–DNA hybridization data, strain A6664 was not included in the description of the novel species.

The proteasome pathway destabilizes Yersinia outer protein E and represses its antihost cell activities

Pathogenic Yersinia spp. neutralize host defense mechanisms by engaging a type III protein secretion system that translocates several Yersinia outer proteins (Yops) into the host cell. Although the modulation of the cellular responses by individual Yops has been intensively studied, little is known about the fate of the translocated Yops inside the cell. In this study, we investigated involvement of the proteasome, the major nonlysosomal proteolytic system in eukaryotic cells, in Yop destabilization and repression. Our data show that inhibition of the proteasome in Yersinia enterocolitica-infected cells selectively stabilized the level of YopE, but not of YopH or YopP. In addition, YopE was found to be modified by ubiquitination. This suggests that the cytotoxin YopE is physiologically subjected to degradation via the ubiquitin-proteasome pathway inside the host cell. Importantly, the increased levels of YopE upon proteasome inhibition were associated with decreased activity of its cellular target Rac. Thus, the GTPase-down-regulating function of YopE is enhanced when the proteasome is inhibited. The stabilization of YopE by proteasome inhibitor treatment furthermore led to aggravation of the cytotoxic YopE effects on the actin cytoskeleton and on host cell morphology. Together, these data show that the host cell proteasome functions to destabilize and inactivate the Yersinia effector protein YopE. This implies the proteasome as integral part of the cellular host immune response against the immunomodulatory activities of a translocated bacterial virulence protein.

Yersinia's stratagem: targeting innate and adaptive immune defense

In contrast to Salmonella and Shigella, enteropathogenic Yersinia species are extracellular multiplying Gram-negative bacteria. This life style requires a sophisticated anti-host strategy, which is implemented by the Yersinia virulence plasmid. This plasmid encodes the type 3 secretion system (injectisome), at least six microinjected anti-host effector proteins, a trimeric coiled coil outer membrane protein (Yersinia adhesin) with cell adhesin and protective functions against complement and defensins, and the released V antigen, which has Toll-like receptor 2 agonist activity.

Nosocomial urosepsis caused by Enterobacter kobei with aberrant phenotype

Enterobacter kobei is the species of the Enterobacter cloacae complex, which is phenotypically most closely related to the species E. cloacae. This is the first report of infection caused by a new biotype of E. kobei. A patient with a history of urinary bladder operation developed a urosepsis with an Enterobacter isolate displaying the E. cloacae phenotype. The isolate was classified to the species E. kobei by sequence analysis of the 16S-rDNA, 4 protein-coding genes and enterobacterial repetitive intergenic consensus (ERIC)-cluster analysis. E. kobei was originally described to be Voges-Proskauer (VP) negative. However, the isolates of the present case were VP-positive. After analyzing 120 biochemical tests included in the API20E and the Biotype 100 systems, 4 biochemical tests were identified potentially differentiating this new biotype from E. cloacae.

Contribution of the major secreted yops of Yersinia enterocolitica O:8 to pathogenicity in the mouse infection model

Pathogenic yersiniae (Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica) harbor a 70-kb virulence plasmid (pYV) that encodes a type III secretion system and a set of at least six effector proteins (YopH, YopO, YopP, YopE, YopM, and YopT) that are injected into the host cell cytoplasm. Yops (Yersinia outer proteins) disturb the dynamics of the cytoskeleton, inhibit phagocytosis by macrophages, and downregulate the production of proinflammatory cytokines, which makes it possible for yersiniae to multiply extracellularly in lymphoid tissue. Y. enterocolitica serotype O:8 belongs to the highly mouse-pathogenic group of yersiniae in contrast to Y. enterocolitica serotype O:9. However, there has been no systematic study of the contribution of Yops to the pathogenicity of Y. enterocolitica O:8 in mice. We generated a set of yop gene deletion mutants of Y. enterocolitica O:8 by using the novel Red cloning procedure. We subsequently analyzed the contribution of yopH, -O, -P, -E, -M, -T, and -Q deletions to pathogenicity after oral and intravenous infection of mice. Here we showed for the first time that a DeltayopT deletion mutant colonizes mouse tissues to a greater extent than the parental strain. The DeltayopO, DeltayopP, and DeltayopE mutants were only slightly attenuated after oral infection since they were still able to colonize the spleen and liver and cause systemic infection. The DeltayopO mutant was lethal for mice, whereas DeltayopP and DeltayopE mutants were successfully eliminated from the spleen and liver 2 weeks after infection. In contrast the DeltayopH, DeltayopM, and DeltayopQ mutants were highly attenuated and not able to colonize the spleen and liver on any of the days tested. The DeltayopH, DeltayopO, DeltayopP, DeltayopE, DeltayopM, and DeltayopQ mutants had only modest defects in the colonization of the small intestine and Peyer's patches. The DeltayopE mutant was eliminated from the small intestine 3 weeks after infection, whereas the DeltayopH, DeltayopP, DeltayopM, and DeltayopQ mutants continued to colonize the small intestine at this time.

Yersinia enterocolitica type III secretion depends on the proton motive force but not on the flagellar motor components MotA and MotB

The flagellum is believed to be the common ancestor of all type III secretion systems (TTSSs). In Yersinia enterocolitica, expression of the flagellar TTSS and the Ysc (Yop secretion) TTSS are inversely regulated. We therefore hypothesized that the Ysc TTSS may adopt flagellar motor components in order to use the pathogenicity-related translocon in a drill-like manner. As a prerequisite for this hypothesis, we first tested a requirement for the proton motive force by both systems using the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP). Motility as well as type III-dependent secretion of Yop proteins was inhibited by CCCP. We deleted motAB, which resulted in an immotile phenotype. This mutant, however, secreted amounts of Yops to the supernatant comparable to those of the wild type. Translocation of Yops into host cells was also not affected by the motAB deletion. Virulence of the mutant was comparable to that of the wild type in the mouse oral infection model. Thus, the hypothesis that the Ysc TTSS might adopt flagellar motor components was not confirmed. The finding that, in addition to consumption of ATP, Ysc TTSS requires the proton motive force is discussed.

Transcriptional responses of murine macrophages to infection with Yersinia enterocolitica

Transcriptional responses of J774 murine macrophage-like cells to infection with Yersinia enterocolitica were evaluated with oligonucleotide microarrays interrogating 12 488 genes and expressed sequence tags. Virulence plasmid (pYV)-cured yersiniae induce a transcriptional programme resembling a general inflammatory response. pYV-carrying yersiniae translocating the Yersinia outer proteins (Yops) impact on this transcriptional programme in two ways: first, by suppressing this inflammatory response and, secondly, by inducing sustained expression of a distinct set of genes with known silencing functions. These tranquilizing patterns of gene expression could be confirmed by real-time reverse transcription polymerase chain reaction, are stable upon reduction in bacterial load and could also be reproduced in BALB/c-derived bone marrow macrophages. Prestimulation of macrophages with interferon (IFN)-gamma, but not with interleukin (IL)-4, induces partial resistance against pYV-mediated transcriptional tranquilization. The first effect, suppression of the inflammatory programme, is mediated by YopP, whereas no YopH- or YopM-regulated genes could be identified under our stringent statistical criteria. The bacterial protein responsible for the second effect, induction of silencing genes, remains elusive. We suggest that Yersinia enterocolitica might use two independent mechanisms to inhibit macrophage inflammatory responses at the transcriptional level.

Highly resistant metabolically deficient dwarf mutant of Escherichia coli is the cause of a chronic urinary tract infection

We present the case of a 68-year-old diabetic woman who has been suffering from chronic urinary tract infections, recurring over a period of at least 5 years, caused by a slowly growing metabolically deficient dwarf mutant (MDD) of Escherichia coli. This MDD strain was auxotrophic for histidine, was resistant to multiple antibiotics, and showed atypical growth behavior. Colonies were tiny on routine media but were able to revert to normal growth after extended incubation. This strain was identified as E. coli by 16S ribosomal DNA sequencing, and virulence factor profiles were determined by PCR. Seven MDD isolates collected over the 5-year period were grown from midstream urine to significant colony counts and shown to belong to the same clonal group by pulsed-field gel electrophoresis and enterobacterial repetitive intergenic consensus PCR. These MDDs were repeatedly misidentified by biochemical methods due to their slow growth and atypical colony morphology. This case highlights the importance of recognizing MDDs of Enterobacteriaceae in patients with chronic infections. To our knowledge this is the first report of an MDD of E. coli causing a chronic urinary tract infection.

Analysis of chaperone-dependent Yop secretion/translocation and effector function using a mini-virulence plasmid of Yersinia enterocolitica

We have constructed a mini-pYV plasmid (pTTSS) harboring the Yersinia type three secretion system (TTSS) and the adhesin yadA on a low-copy vector. Using this system we could demonstrate for the first time that YopO, YopP, YopM, and YopQ do not require any of the known or orphan chaperones for efficient secretion/translocation. Y. enterocolitica harboring pTTSS, (WA-C(pTTSS)) was able to secrete and translocate single Yop effector proteins in trans. WA-C(pTTSS) proved to be stable and secretion of Yops was Ca2+ and temperature dependent as is the case for the parental strain. This shows that all genes necessary for translocation and expression of the Ca(2+)-dependent phenotype are contained within the cloned region. In contrast to previously published multiple yop mutants which were constructed by sequential deletion of yops, our system which harbors only the TTSS region without yops, chaperones, and unknown ORFs can be sequentially complemented with yops and sycs of choice. WA-C(pTTSS) was able to translocate YopE, YopM and YopT into HeLa cells as demonstrated by Western blotting. Translocation of YopE and YopT was strictly dependent on the presence of their respective chaperones, whereas YopM did not require a chaperone for translocation. WA-C(pTTSS) harboring yopT and sycT was shown to translocate active YopT by demonstrating modification of the small GTP-binding protein RhoA. This shows for the first time that RhoA modification is strictly dependent on YopT and does not require additional effector Yops. WA-C(pTTSS) harboring YopP was shown to induce apoptosis. This system is ideal to study chaperone-dependent Yop secretion/ translocation without the background of other effector Yops (YopE, YopM, YopO, YopP, YopT, YopH), chaperones (SycE, SycH, SycT) and unknown ORFs. In addition this system can secrete heterologous proteins fused to the N-terminal secretion/translocation domain of YopE.

"Staphylococcus pettenkoferi," a novel staphylococcal species isolated from clinical specimens

In this report we describe a novel species of coagulase-negative novobiocin susceptible staphylococci obtained from an epidemiologically unrelated blood culture and a wound infection. These isolates significantly differed from all other validated Staphylococcus species based on phenotypic characteristics and 16S rRNA gene sequencing. Both isolates had identical 16S rRNA sequences and phylogenetic trees constructed from evolutionary distances showed that this species formed a distinct and deep subline that was most closely related to members of the Staphylococcus saprophyticus cluster group (S. kloosii, S. gallinarum, S. arlettae, S. saprophyticus, S. xylosus, S. equorum, S. succinus and S. cohnii) and Staphylococcus auricularis. Furthermore these strains could each be distinguished from all other staphylococci based on at least one phenotypic trait. Therefore we propose the designation of "Staphylococcus pettenkoferi" a novel species of coagulase-negative staphylococci.

YopE of Yersinia, a GAP for Rho GTPases, selectively modulates Rac-dependent actin structures in endothelial cells

Yersinia spp. inject effector proteins (Yersinia outer proteins, Yops) into target cells via a type III secretion apparatus. The effector YopE was recently shown to possess GAP activity towards the Rho GTPases RhoA, Rac and CDC42 in vitro. To investigate the intracellular, 'in vivo' targets of YopE we generated a Yersinia enterocolitica strain [WA(pYLCR+E)] that injects 'life-like' amounts of YopE as only effector. Primary human umbilical vein endothelial cells (HUVEC) were infected with WA(pYLCR+E) and were then stimulated with: (i) bradykinin to induce actin microspikes followed by ruffles as an assay for CDC42 activity followed by CDC42 stimulated Rac activity; (ii) sphingosine-1-phosphate to form ruffles by direct Rac activation; or (iii) thrombin to generate actin stress fibres through Rho activation. In WA(pYLCR+E)-infected HUVEC microspike formation stimulated with bradykinin remained intact but the subsequent development of ruffles was abolished. Furthermore, ruffle formation after stimulation with sphingosine-1-phosphate or thrombin induced production of stress fibres was unaltered in the infected cells. These data suggest that YopE is able to inhibit Rac- but not Rho- or CDC42-regulated actin structures and, more specifically, that YopE is capable of blocking CDC42Hs dependent Rac activation but not direct Rac activation in HUVEC. This provides evidence for a considerable specificity of YopE towards selective Rac-mediated signalling pathways in primary target cells of Yersinia.

Yersinia outer protein P of Yersinia enterocolitica simultaneously blocks the nuclear factor-kappa B pathway and exploits lipopolysaccharide signaling to trigger apoptosis in macrophages

Exposure of macrophages to bacteria or LPS mediates activation of signaling pathways that induce expression of self defense-related genes. Pathogenic Yersinia species impair activation of transcription factor NF-kappaB and trigger apoptosis in macrophages. In this study, we dissected the mechanism of apoptosis induction by Yersinia. Selectively, Yersinia enterocolitica strains producing the effector protein Yersinia outer protein P (YopP) hampered NF-kappaB activation and subsequently conferred apoptosis to J774A.1 macrophages. Thereby, YopP bound and inhibited the macrophage NF-kappaB-activating kinase IKKbeta. YopP- and Yersinia-, but not Salmonella-induced apoptosis was specifically prevented by transient overexpression of NF-kappaB p65, giving evidence that YopP mediates cell death by disrupting the NF-kappaB signaling pathway. Transfection of J774A.1 macrophages with YopP induced a moderate, but significant degree of apoptosis (40-50% of transfected cells). This effect was strongly enhanced by additional initiation of LPS signaling (80-90%), indicating a synergism between LPS-induced signal transduction and inhibition of NF-kappaB by YopP. This reflects a strategy of a bacterial pathogen that takes advantage of LPS, serving as cofactor, to impair the macrophage.

Cloning and characterization of the gene encoding periplasmic 2',3'-cyclic phosphodiesterase of Yersinia enterocolitica O:8

The gene encoding periplasmic 2',3'-cyclic phosphodiesterase in Yersinia enterocolitica O:8 (designated cpdB), was cloned and expressed in Escherichia coli. This enzyme enables Y. enterocolitica to grow on 2',3'-cAMP as a sole source of carbon and energy. Sequencing and analysis of a 3 kb ECO:RI fragment containing the cpdB gene revealed an open reading frame of 1179 bp, corresponding to a protein with a molecular mass of 71 kDa. The first 25 amino acid residues show features of a typical prokaryotic signal sequence. The predicted molecular mass of the mature peptide is therefore in agreement with the molecular mass estimated by SDS gel electrophoresis (68 kDa). The putative cpdB promoter region contains two possible -10 and -35 regions. Furthermore, the 5' untranslated region contains sequences with significant homology to the cyclic AMP-cyclic AMP receptor protein binding site and the sigma(28) consensus. This region is interrupted by an enterobacterial repetitive intergenic consensus (ERIC) sequence. Deletion of the ERIC element from the cpdB promoter region had no effect on cpdB expression. In the 3' untranslated region, a possible rho-independent transcriptional terminator was identified. The deduced amino acid sequence of the Y. enterocolitica CpdB protein shows 76% identity with CpdB of Salmonella typhimurium and E. coli. CpdB of Y. enterocolitica is exported to the periplasmic space. An isogenic Y. enterocolitica cpdB mutant strain, constructed by allelic exchange, was no longer able to grow on 2',3'-cAMP as sole source of carbon and energy. The CpdB mutant showed no significant change in virulence in an oral and intravenous mouse infection model.

The Yersinia Ser/Thr protein kinase YpkA/YopO directly interacts with the small GTPases RhoA and Rac-1

Pathogenic bacteria of the genus Yersinia counteract host defense by interfering with eukaryotic signal transduction pathways. YpkA of Yersinia pseudotuberculosis shares significant homology with eukaryotic Ser/Thr protein kinases, is translocated into the host cell and has been shown to be an essential virulence factor in a mouse infection model. In this study, we identify the small GTPases RhoA and Rac-1 as eukaryotic binding partners of YpkA and its homolog YopO of Yersinia enterocolitica. We demonstrate that the interaction is independent of phosphorylation of YpkA and nucleotide loading state of the GTPases. The interaction with RhoA and Rac-1 might provide an important clue to how YpkA interferes with eukaryotic signaling on a molecular level.