Role of Yops in inhibition of phagocytosis and killing of opsonized Yersinia enterocolitica by human granulocytes

Plague Prevention and Therapy: Perspectives on Current and Future Strategies

Plague, caused by the bacterial pathogen Yersinia pestis, is a vector-borne disease that has caused millions of human deaths over several centuries. Presently, human plague infections continue throughout the world. Transmission from one host to another relies mainly on infected flea bites, which can cause enlarged lymph nodes called buboes, followed by septicemic dissemination of the pathogen. Additionally, droplet inhalation after close contact with infected mammals can result in primary pneumonic plague. Here, we review research advances in the areas of vaccines and therapeutics for plague in context of Y. pestis virulence factors and disease pathogenesis. Plague continues to be both a public health threat and a biodefense concern and we highlight research that is important for infection mitigation and disease treatment.

Invasiveness of the Yersinia pestis ail protein contributes to host dissemination in pneumonic and oral plague

Yersinia pestis, a Gram-negative bacterium, is the etiologic agent of plague. A hallmark of Y. pestis infection is the organism's ability to rapidly disseminate through an animal host. Y. pestis expresses the outer membrane protein, Ail (Attachment invasion locus), which is associated with host invasion and serum resistance. However, whether Ail plays a role in host dissemination remains unclear. In this study, C57BL/6J mice were challenged with a defined Y. pestis strain, KimD27, or an isogenic ail-deleted mutant derived from KimD27 via metacarpal paw pad inoculation, nasal drops, orogastric infection, or tail vein injection to mimic bubonic, pneumonic, oral, or septicemic plague, respectively. Our results showed that ail-deleted Y. pestis KimD27 lost the ability to invade host cells, leading to failed host dissemination in the pneumonic and oral plague models but not in the bubonic or septicemic plague models, which do not require invasiveness. Therefore, this study demonstrated that whether Ail plays a role in Y. pestis pathogenesis depends on the infection route.

Yersinia pseudotuberculosis-derived adhesins

Around fifteen surface components referred to adhesins have been identified in Yersinia pseudotuberculosis combining primarily microbiological, molecular and genetic, as well as immunochemical and biophysical methods. Y. pseudotuberculosis-derived adhesins vary in structure and chemical composition but they are mainly presented by protein molecules. Some of them were shown to participate not only in adhesive but in other pathogen-related physiological functions in the host-parasite interplay. Adhesins can mediate bacterial adhesion to eukaryotic cell either directly or via the extracellular matrix components. These adhesion molecules are encoded by chromosomal DNA excepting YadA protein which gene is located in the calcium-dependence plasmid pYV common for pathogenic yersisniae. An optimum temperature for adhesin biosynthesis is located close to the body temperature of warm-blooded animals; however, at low temperature only invasin InvA, full-length smooth lipopolysaccharide and porin OmpF are produced in Y. pseudotuberculosis. Several adhesins (Psa, InvA) can be expressed at low pH (corresponds to intracellular content), thereby defining pathogenic yersiniae as facultative intracellular parasites. Three human Yersinia genus pathogens differ by ability to produce adhesins. Y. pseudotuberculosis adherence to host cells or extracellular matrix components is determined by a cumulative adhesion-based activity, which expression depends on chemical composition and physicochemical environmental conditions. It’s proposed that at the initial stage of infectious process adherence of Y. pseudotuberculosis to intestinal epithelium is mediated by InvA protein and “smooth” LPS form. These adhesins are produced in bacterial cells at low (lower than 30°С) temperature occurring in environment from which a pathogen invades into the host. At later stages of pathogenesis, after penetrating through intestinal epithelium, bacterial cells produce other adhesins, which promote survival and dissemination primarily into the mesenteric lymph nodes and, possibly, liver and spleen. At later stages of pathogenesis, after penetrating through intestinal epithelium, bacterial cells produce other adhesins, which promote survival and dissemination primarily into the mesenteric lymph nodes and, perhaps, liver and spleen. Qualitative and quantitative spectrum of Y. pseudotuberculosis adhesins is determined by environmental parameters (intercellular space, intracellular content within the diverse eukaryotic cells).

Going around in circles: virulence plasmids in enteric pathogens

Plasmids have a major role in the development of disease caused by enteric bacterial pathogens. Virulence plasmids are usually large (>40 kb) low copy elements and encode genes that promote host-pathogen interactions. Although virulence plasmids provide advantages to bacteria in specific conditions, they often impose fitness costs on their host. In this Review, we discuss virulence plasmids in Enterobacteriaceae that are important causes of diarrhoea in humans, Shigella spp., Salmonella spp., Yersinia spp and pathovars of Escherichia coli. We contrast these plasmids with those that are routinely used in the laboratory and outline the mechanisms by which virulence plasmids are maintained in bacterial populations. We highlight examples of virulence plasmids that encode multiple mechanisms for their maintenance (for example, toxin-antitoxin and partitioning systems) and speculate on how these might contribute to their propagation and success.

Yersinia pseudotuberculosis Blocks Neutrophil Degranulation

Neutrophils are essential components of immunity and are rapidly recruited to infected or injured tissue. Upon their activation, neutrophils release granules to the cell's exterior, through a process called degranulation. These granules contain proteins with antimicrobial properties that help combat infection. The enteropathogenic bacterium Yersinia pseudotuberculosis successfully persists as an extracellular bacterium during infection by virtue of its translocation of virulence effectors (Yersinia outer proteins [Yops]) that act in the cytosol of host immune cells to subvert phagocytosis and proinflammatory responses. Here, we investigated the effect of Y. pseudotuberculosis on neutrophil degranulation upon cell contact. We found that virulent Y. pseudotuberculosis was able to prevent secondary granule release. The blocking effect was general, as the release of primary and tertiary granules was also reduced. Degranulation of secondary granules was also blocked in primed neutrophils, suggesting that this mechanism could be an important element of immune evasion. Further, wild-type bacteria conferred a transient block on neutrophils that prevented their degranulation upon contact with plasmid-cured, avirulent Y. pseudotuberculosis and Escherichia coli Detailed analyses showed that the block was strictly dependent on the cooperative actions of the two antiphagocytic effectors, YopE and YopH, suggesting that the neutrophil target structures constituting signaling molecules needed to initiate both phagocytosis and general degranulation. Thus, via these virulence effectors, Yersinia can impair several mechanisms of the neutrophil's antimicrobial arsenal, which underscores the power of its virulence effector machinery.

Yersinia virulence factors - a sophisticated arsenal for combating host defences

The human pathogens Yersinia pseudotuberculosis and Yersinia enterocolitica cause enterocolitis, while Yersinia pestis is responsible for pneumonic, bubonic, and septicaemic plague. All three share an infection strategy that relies on a virulence factor arsenal to enable them to enter, adhere to, and colonise the host while evading host defences to avoid untimely clearance. Their arsenal includes a number of adhesins that allow the invading pathogens to establish a foothold in the host and to adhere to specific tissues later during infection. When the host innate immune system has been activated, all three pathogens produce a structure analogous to a hypodermic needle. In conjunction with the translocon, which forms a pore in the host membrane, the channel that is formed enables the transfer of six ‘effector’ proteins into the host cell cytoplasm. These proteins mimic host cell proteins but are more efficient than their native counterparts at modifying the host cell cytoskeleton, triggering the host cell suicide response. Such a sophisticated arsenal ensures that yersiniae maintain the upper hand despite the best efforts of the host to counteract the infecting pathogen.

Spatially distinct neutrophil responses within the inflammatory lesions of pneumonic plague

During pneumonic plague, the bacterium Yersinia pestis elicits the development of inflammatory lung lesions that continue to expand throughout infection. This lesion development and persistence are poorly understood. Here, we examine spatially distinct regions of lung lesions using laser capture microdissection and transcriptome sequencing (RNA-seq) analysis to identify transcriptional differences between lesion microenvironments. We show that cellular pathways involved in leukocyte migration and apoptosis are downregulated in the center of lung lesions compared to the periphery. Probing for the bacterial factor(s) important for the alteration in neutrophil survival, we show both in vitro and in vivo that Y. pestis increases neutrophil survival in a manner that is dependent on the type III secretion system effector YopM. This research explores the complexity of spatially distinct host-microbe interactions and emphasizes the importance of cell relevance in assays in order to fully understand Y. pestis virulence.

Yersinia pestis is a high-priority pathogen and continues to cause outbreaks worldwide. The ability of Y. pestis to be transmitted via respiratory droplets and its history of weaponization has led to its classification as a select agent most likely to be used as a biological weapon. Unrestricted bacterial growth during the initial preinflammatory phase primes patients to be infectious once disease symptoms begin in the proinflammatory phase, and the rapid disease progression can lead to death before Y. pestis infection can be diagnosed and treated. Using in vivo analyses and focusing on relevant cell types during pneumonic plague infection, we can identify host pathways that may be manipulated to extend the treatment window for pneumonic plague patients.

¹H, ¹⁵N, and ¹³C backbone resonance assignments for the Yersinia protein tyrosine phosphatase YopH

YopH is a protein tyrosine phosphatase that functions as a required virulence factor in Yersinia. Here we report the backbone resonance assignments for a point mutant of the C-terminal catalytic domain of YopH.

Yersinia pseudotuberculosis uses Ail and YadA to circumvent neutrophils by directing Yop translocation during lung infection

A Yersinia pseudotuberculosis (Yptb) murine model of lung infection was previously developed using the serotype III IP2666NdeI strain, which robustly colonized lungs but only sporadically disseminated to the spleen and liver. We demonstrate here that a serotype Ib Yptb strain, IP32953, colonizes the lungs at higher levels and disseminates more efficiently to the spleen and liver compared with IP2666NdeI . The role of adhesins was investigated during IP32953 lung infection by constructing isogenic Δail, Δinv, ΔpsaE and ΔyadA mutants. An IP32953ΔailΔyadA mutant initially colonized but failed to persist in the lungs and disseminate to the spleen and liver. Yptb expressing these adhesins selectively bound to and targeted neutrophils for translocation of Yops. This selective targeting was critical for virulence because persistence of the ΔailΔyadA mutant was restored following intranasal infection of neutropenic mice. Furthermore, Ail and YadA prevented killing by complement-mediated mechanisms during dissemination to and/or growth in the spleen and liver, but not in the lungs. Combined, these results demonstratethat Ail and YadA are critical, redundant virulence factors during lung infection, because they thwart neutrophils by directing Yop-translocation specifically into these cells.

Yersinia infection tools-characterization of structure and function of adhesins

Among the seventeen species of the Gram-negative genus Yersinia, three have been shown to be virulent and pathogenic to humans and animals-Y. enterocolitica, Y. pseudotuberculosis, and Y. pestis. In order to be so, they are armoured with various factors that help them adhere to tissues and organelles, cross the cellular barrier and escape the immune system during host invasion. The group of proteins that mediate pathogen-host interactions constitute adhesins. Invasin, Ail, YadA, YadB, YadC, Pla, and pH 6 antigen belong to the most prominent and best-known Yersinia adhesins. They act at different times and stages of infection complementing each other by their ability to bind a variety of host molecules such as collagen, fibronectin, laminin, β1 integrins, and complement regulators. All the proteins are anchored in the bacterial outer membrane (OM), often forming rod-like or fimbrial-like structures that protrude to the extracellular milieu. Structural studies have shown that the anchor region forms a β-barrel composed of 8, 10, or 12 antiparallel β-strands. Depending on the protein, the extracellular part can be composed of several domains belonging to the immunoglobulin fold superfamily, or form a coiled-coil structure with globular head domain at the end, or just constitute several loops connecting individual β-strands in the β-barrel. Those extracellular regions define the activity of each adhesin. This review focuses on the structure and function of these important molecules, and their role in pathogenesis.

The impact of Toll-like receptors on bacterial virulence strategies

The mammalian immune system has evolved in the presence of microbes, both pathogenic and commensal. The consequences of microbial recognition by the host has led to the development of compensatory mechanisms by both the host and microbe to either resist or tolerate the existence of the other. In this review we discuss examples of this co-evolutionary relationship. Because of space considerations and for conceptual clarity, we have focused on detection of bacteria by the Toll-like receptor (TLR) family and highlight examples of bacterial strategies to evade, subvert and in some cases even utilize these receptors.

Role of YopK in Yersinia pseudotuberculosis resistance against polymorphonuclear leukocyte defense

The enteropathogen Yersinia pseudotuberculosis can survive in the harsh environment of lymphoid compartments that abounds in immune cells. This capacity is dependent on the plasmid-encoded Yersinia outer proteins (Yops) that are delivered into the host cell via a mechanism involving the Yersinia type III secretion system. We show that the virulence protein YopK has a role in the mechanism by which Y. pseudotuberculosis avoids the polymorphonuclear leukocyte or neutrophil (PMN) defense. A yopK mutant, which is attenuated in the mouse infection model, where it fails to cause systemic infection, was found to colonize Peyer's patches and mesenteric lymph nodes more rapidly than the wild-type strain. Further, in mice lacking PMNs, the yopK mutant caused full disease with systemic spread and typical symptoms. Analyses of effects on PMNs revealed that both the wild-type strain and the yopK mutant inhibited internalization and reactive oxygen species production, as well as neutrophil extracellular trap formation by PMNs. However, the wild-type strain effectively avoided induction of PMN death, whereas the mutant caused a necrosis-like PMN death. Taken together, our results indicate that YopK is required for the ability of Yersinia to resist the PMN defense, which is critical for the virulence of the pathogen. We suggest a mechanism whereby YopK functions to prevent unintended Yop delivery and thereby PMN disruption, resulting in necrosis-like cell death, which would enhance the inflammatory response favoring the host.

Adhesins of human pathogens from the genus Yersinia

Bacteria of the Gram-negative genus Yersinia are environmentally ubiquitous. Three species are of medical importance: the intestinal pathogens Y. enterocolitica and Y. pseudotuberculosis, and the plague bacillus Y. pestis. The two former species, spread by contaminated food or water, cause a range of gastrointestinal symptoms and, rarely, sepsis. On occasion, the primary infection is followed by autoimmune sequelae such as reactive arthritis. Plague is a systemic disease with high mortality. It is a zoonosis spread by fleas, or more rarely by droplets from individuals suffering from pneumonic plague. Y. pestis is one of the most virulent of bacteria, and recent findings of antibiotic-resistant strains together with its potential use as a bioweapon have increased interest in the species. In addition to being significant pathogens in their own right, the yersiniae have been used as model systems for a number of aspects of pathogenicity. This chapter reviews the molecular mechanisms of adhesion in yersiniae. The enteropathogenic species share three adhesins: invasin, YadA and Ail. Invasin is the first adhesin required for enteric infection; it binds to β(1) integrins on microfold cells in the distal ileum, leading to the ingestion of the bacteria and allows them to cross the intestinal epithelium. YadA is the major adhesin in host tissues. It is a multifunctional protein, conferring adherence to cells and extracellular matrix components, serum and phagocytosis resistance, and the ability to autoagglutinate. Ail has a minor role in adhesion and serum resistance. Y. pestis lacks both invasin and YadA, but expresses several other adhesins. These include the pH 6 antigen and autotransporter adhesins. Also the plasminogen activator of Y. pestis can mediate adherence to host cells. Although the adhesins of the pathogenic yersiniae have been studied extensively, their exact roles in the biology of infection remain elusive.

Viability and survival capability of quinolone-resistant uropathogenic Escherichia coli

Uropathogenic strains of E. coli isolated from urine of patients with urinary tract infections were tested for antibiotic sensitivity using bio-Merieux kits and ATB-UR 5 expression system. The virulence of strains was evaluated by serum bactericidal assay, macrophage “killing” and bacterial adhesive tests. Survival capability of strains was assessed under starvation in saline. The results showed that quinolone-resistant uropathogenic strains of E. coli exhibit significantly reduced adhesive potential but relatively high resistance to serum and macrophage bactericidity. In contrast to laboratory strains, the quinolone-resistant uropathogenic clinical isolate demonstrated increased viability during starvation in saline. Our study suggests that quinolone-resistant uropathogenic strains are highly adaptable clones of E. coli, which can exhibit compensatory viability potential under unfavorable conditions. The clinical occurrence of such phenotypes is likely to contribute to the survival, persistence and spread strategy of resistant bacteria.

Composition and properties of biologically active pectic polysaccharides from leek (Allium porrum)

BACKGROUND

Leek (Allium porrum) is very commonly used vegetable in Bulgaria and is distinctive with high content of bioactive components. Previously we obtained five crude pectic polysaccharides from leek through consecutive extraction. Some of them appeared to be good stimulators of the immune system. Schols and Voragen investigated the composition of modified hairy regions of pectic polysaccharides isolated from leek cell walls. Samuelson et al. identified the polysaccharide structures encountered in hairy regions as bioactive. The aim of this work was to study the isolation, composition and biological activities of pectic polysaccharides from leek.

RESULTS

Two pectic polysaccharides from leek were isolated through consecutive water and acid extraction. The water extractable pectin had higher polyuronic content, higher protein content and lower neutral sugar content. It was found that next to galacturonic acid they also contain glucuronic acid in ratio 9:1 for the water- and 3:1 for the acid-extractable polysaccharide. The main neutral sugar was galactose. The water-extractable pectic polysaccharide had higher molecular weight (10(6) Da) and homogeneity. It was shown that the pectic polysaccharides from leek have considerable immunostimulating activities.

CONCLUSION

Leek polysaccharides have relatively high galacturonic and glucuronic acid content and are distinguished with high biological activity.

Human polymorphonuclear neutrophil responses to Burkholderia pseudomallei in healthy and diabetic subjects

The major predisposing factor for melioidosis is diabetes mellitus, but no immunological mechanisms have been investigated to explain this. In this study, polymorphonuclear neutrophil (PMN) responses to Burkholderia pseudomallei, the causative agent of melioidosis, in healthy and diabetic Thai subjects were determined by flow cytometry. The results showed that B. pseudomallei displayed reduced uptake by PMNs compared to Salmonella enterica serovar Typhimurium and Escherichia coli. Additionally, intracellular survival of B. pseudomallei was detected throughout a 24-h period, indicating the intrinsic resistance of B. pseudomallei to killing by PMNs. Moreover, PMNs from diabetic subjects displayed impaired phagocytosis of B. pseudomallei, reduced migration in response to interleukin-8, and an inability to delay apoptosis. These data show that B. pseudomallei is intrinsically resistant to phagocytosis and killing by PMNs. These observations, together with the impaired migration and apoptosis in diabetes mellitus, may explain host susceptibility in melioidosis.

Attenuation and preserved immunogenic potential of Yersinia pseudotuberculosis mutant strains evidenced in oral pig model

Experimental oral infection of pigs with a parental Yersinia pseudotuberculosis strain pIB102, serotype O:3 and two mutant isogenic strains - pIB155,DeltayopK and pIB44,DeltaypkA has been carried out. Clinical findings, microbiological and immunological parameters were examined in dynamics from day 7 to day 60 post-infection (p.i.). All types of infections ran asymptomatically, without hyperthermia, loss of appetite, etc. Experiments on the blood parameters demonstrated a transient leucocytosis with lymphocytosis and monocytosis better expressed after yopK infection. Even though pig is usually known as a reservoir of yersiniae, bacterial colonization was found in mesenterial lymph nodes and tonsils on day 7, respectively 14 p.i. with parental strain, and only in tonsils on day 14 p.i. with both mutant strains. The augmented sensitivity of mutants to the bactericidal effect of leukocytes and blood sera is the characteristic feature of attenuation in their pathogenicity, compared to the parental strain. Comparative in vitro experiments on the immune response and immunostimulating capacity of Y. pseudotuberculosis mutant strains verify their preserved immunogenic potential, predominantly in case of yopK. Hyperplasia and strong activation of the lymph tissue of Peyer's patches, mesenterial lymph nodes, tonsils and spleen of pigs challenged with both mutant strains were proved as immunomorphological rearrangements. The results obtained give the reason to claim that the genetically constructed yopK null mutant strain is significantly attenuated but is still immunogenic and has the potential for a live vaccine carrier strain.

Yersinia pestis type III secretion system-dependent inhibition of human polymorphonuclear leukocyte function

Human polymorphonuclear leukocytes (PMNs, or neutrophils) are the primary innate host defense against invading bacterial pathogens. Neutrophils are rapidly recruited to sites of infection and ingest microorganisms through a process known as phagocytosis. Following phagocytosis by human PMNs, microorganisms are killed by reactive oxygen species (ROS) and microbicidal products contained within granules. Yersinia pestis, the causative agent of plague, is capable of rapid replication and dissemination from sites of infection in the host. Although Y. pestis survives in macrophages, the bacterial fate following interaction with human PMNs is less clear. The ability of Y. pestis to inhibit phagocytosis by human PMNs was assessed by differential fluorescence microscopy and was shown to be dependent on expression of the type III secretion system (TTSS). Previous studies have demonstrated that TTSS expression in enteropathogenic Yersinia spp. also inhibits the respiratory burst in PMNs and macrophages, and we show here that human PMN ROS production is similarly repressed by Y. pestis. However, exclusion of uningested TTSS-expressing Y. pestis with gentamicin revealed that intracellular bacteria are eliminated by human PMNs, similar to bacteria lacking the TTSS. In summary, our results suggest that the Y. pestis TTSS contributes to extracellular survival following interactions with human PMNs and that the intracellular fate is independent of TTSS inhibition of neutrophil ROS production.

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.

Experimental pig yersiniosis to assess attenuation of Yersinia enterocolitica O:8 mutant strains

An experimental oral pig model was used to assess the pathogenic and immunogenic potential of Yersinia enterocolitica serotype O:8 wild-type strain 8081-L2 and its lipopolysaccharide (LPS) mutant derivatives: a spontaneous rough mutant 8081-R2, strain 8081-DeltawzzGB expressing O-antigen with uncontrolled chain lengths, and strain 8081-wbcEGB expressing semirough LPS with only one O-unit. Microbiological and immunological parameters of the infected pigs were followed from day 7 to 60 postinfection. The wild-type and all LPS mutant strains persisted in the lymphoid tissue of tonsils and small intestines, causing asymptomatic infection without any pathological changes. Although the pig is known as a reservoir of Yersiniae, a precise analysis of pathogenic and immunogenic parameters based on different in vitro tests (hematological response, killing ability of leukocytes and blood sera, antibody response, hydrogen peroxide production by macrophages, classical and alternative pathways of complement activation), revealed significant attenuation in the pathogenicity of the LPS mutant strains but not the loss of immunogenic potential. In comparison with the other strains, strain 8081-DeltawzzGB demonstrated more continuous leucocytosis with monocytosis, higher invasive potential, significant activation of hydrogen peroxide production by macrophages and an effective immunoglobulin G immune response accompanied by relevant histological immunomorphological rearrangements.

Modulation of complement activityin Vitro andin Vivo byYersinia wild and mutant strains

The ability of released proteins (Yops) and surface lipopolysaccharides (LPS) from the wild-type strain Yersinia enterocolitica 8081-L2, serotype 0:8 to influence the complement activity was determined. Yops and LPS from wild-type and mutant strains showed different ability to affect the classical pathway (CP) functional complement activity in vitro. The serum CP activity was inhibited during the infection induced with six Y. enterocolitica and three Y. pseudotuberculosis strains in rabbits. The changed complement activity might be of importance for the course of Yersinia infections.

Tyrosine phosphatase MptpA of Mycobacterium tuberculosis inhibits phagocytosis and increases actin polymerization in macrophages

Protein tyrosine phosphatases from several microorganisms have been shown to play a role as virulence factors by modifying the phosphorylation/dephosphorylation equilibrium in cells of their host. Two tyrosine phosphatases, MptpA and MptpB, secreted by Mycobacterium tuberculosis, have been identified. Expression of MptpA is upregulated upon infection of monocytes, but its role in host cells has not been elucidated. A eukaryotic expression vector containing the mptpA cDNA has been transfected into macrophages. We report that MptpA reduced phagocytosis of mycobacteria, opsonized zymosan or zymosan, but had no effect on phagocytosis of IgG-coated particles. We also noted that the presence of F-actin at the surface of phagosomes containing opsonized zymosan was significantly increased in cells expressing MptpA. In the presence of recombinant MptpA, the process of actin polymerization at the surface of isolated phagosomes was increased; this was not the case in the presence of the phosphatase-dead mutant MptpA(C11S). MptpA had no effect when IgG-coated particles were present inside isolated phagosomes. These results indicate that, like other tyrosine phosphatases of pathogens, MptpA plays a role in phagocytosis and actin polymerization. However, MptpA had no effect on IgG particles, suggesting that its putative substrate(s) is not linked to the signaling pathways of Fcgamma receptors.

Combined immunomodulating effects of BCG and Lentinan after intranasal application in guinea pigs

The ability of a Shiitake (Lentinus edodes) medical mushroom-derived bioactive polymer Lentinan (Ajinomoto, Japan) to modulate the immune response makes it a potential candidate for combination therapy with BCG, or as adjunct for BCG vaccination, especially in high-risk individuals. We studied the combined immune-potential effectiveness of intranasal application of Lentinan (at a dose of 1 mg/kg, three times at 2-day intervals), followed by administration of BCG (strain Sofia SL-222 at a dose of 1 x 10(8) CFU, once) in guinea pigs. Samples of broncho-alveolar lavage fluid, as well as tissue fragments of lungs, spleens and lymph nodes were obtained from four groups (combined treatment with Lentinan and BCG; only with Lentinan; only with BCG; control with saline) of animals at different intervals--1, 14 and 45 days after last treatment and were evaluated by several parameters (establishing the number, H2O2 and nitrite production, and killing ability against Mycobacterium tuberculosis and Staphylococcus aureus of alveolar macrophages; spleen index, BCG CFU in spleens and histomorphological observations). Our attention was focused both on local effects in lungs, and systematical effects in reticuloendothelial system. The results indicate that intranasal application of BCG alone, or in combination with Lentinan induced high level of alveolar macrophage activation. Pre-treatment with Lentinan enhanced the local immunohistological response to BCG in lung and reduced the generalized side effects.

Cellular mechanisms of bacterial internalization counteracted by Yersinia

Upon host-cell contact, human pathogenic Yersinia species inject Yop virulence effectors into the host through a Type III secretion-and-translocation system. These virulence effectors cause a block in phagocytosis (YopE, YopT, YpkA, and YopH) and suppression of inflammatory mediators (YopJ). The Yops that block phagocytosis either interfere with the host cell actin regulation of Rho GTPases (YopE, YopT, and YpkA) or specifically and rapidly inactivate host proteins involved in signaling from the receptor to actin (YopH). The block in uptake has been shown to be activated following binding to Fc, Complement, and beta1-integrin receptors in virtually any kind of host cell. Thus, the use of Yersinia as a model system to study Yersinia-host cell interactions provides a good tool to explore signaling pathways involved in phagocytosis.

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

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

Experimental infections with wild and mutant Yersinia pseudotuberculosis strains in rabbits

Experimental oral infections of rabbits with a wild-type Yersinia pseudotuberculosis strain (pIB102), and two null-mutants (yopK and ypkA) were carried out with the aim to explore the possibility to use mutant strains of Y. pseudotuberculosis as live carrier vaccine strains. The infectious process of the three strains proceed with passing hyperthermia, leucocytosis with granulocytosis, moderate monocytosis and a transient lymphopenia, better demonstrated at mutant strain infections. Short-term bacterial dissemination into the brain and viscera was observed at yopK infection. An augmented resistance to bactericidal activity of leucocytes at the initial phase of infection was followed by an increased sensitivity discovered earlier in case of yopK strain accompanied by at least 70- and 20-fold, respectively, for ypkA lower virulence for mice. The level of attenuation of yopK was accompanied by significant Yersinia specific IgG and IgM antibody response. Inflammatory foci were found by morphological examination in brain, lung and small intestines after infection with the wild-type strain, while such foci were only observed in brain and mesenterial lymph nodes after infection with the yopK mutant. After infection with the ypkA mutant foci were found in brain and spleen of the infected animals. Morphological changes in the lymphatic tissue of rabbits infected with mutant strains were consistent with induction of immunogenesis. The data suggest that genetically constructed yopK null-mutant exhibits characteristics that makes the strain suitable to be used as a live carrier vaccine to deliver heterologous antigens.

Protective activity of Lentinan in experimental tuberculosis

Protective effects of Lentinan (Ajinomoto, Japan) against Mycobacterium tuberculosis infection were studied by in vitro and in vivo mouse models. The effectiveness of Lentinan administrated intraperitoneally (i.p.) before infection at a dose of 1 mg/kg three times at 2-day intervals was monitored in vivo by several parameters (body temperature; spleen weight; CFU counts of M. tuberculosis in spleen, liver and lung; and histomorphological observations). Peritoneal macrophages obtained from animals treated with Lentinan were greatly stimulated, as assayed by establishing their number, acid phosphatase activity, H2O2 production and killing ability against M. tuberculosis in vitro. The in vivo model demonstrated that administration of Lentinan before infection can mobilize host defense potential and reduce mycobacterial infection.

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.

YscP and YscU regulate substrate specificity of the Yersinia type III secretion system

Pathogenic Yersinia species use a type III secretion system to inhibit phagocytosis by eukaryotic cells. At 37 degrees C, the secretion system is assembled, forming a needle-like structure on the bacterial cell surface. Upon eukaryotic cell contact, six effector proteins, called Yops, are translocated into the eukaryotic cell cytosol. Here, we show that a yscP mutant exports an increased amount of the needle component YscF to the bacterial cell surface but is unable to efficiently secrete effector Yops. Mutations in the cytoplasmic domain of the inner membrane protein YscU suppress the yscP phenotype by reducing the level of YscF secretion and increasing the level of Yop secretion. These results suggest that YscP and YscU coordinately regulate the substrate specificity of the Yersinia type III secretion system. Furthermore, we show that YscP and YscU act upstream of the cell contact sensor YopN as well as the inner gatekeeper LcrG in the pathway of substrate export regulation. These results further strengthen the strong evolutionary link between flagellar biosynthesis and type III synthesis.

Effects of intraperitoneal and intranasal application of Lentinan on cellular response in rats

Lentinan (Ajinomoto, Japan) was administrated intraperitoneally (i.p.) and intranasally (i.n.) at different doses (1, 5 and 10 mg/kg) to rats. Effectiveness of Lentinan treatment was evaluated by comparative testing of cell activation (establishing the number, glycolytic and acid phosphatase activity, H2O2 production and killing ability against Salmonella enteritidis and Staphylococcus aureus) at two different compartments--peritoneal and broncho-alveolar cavities. The results indicated that Lentinan induced high-grade activation of peritoneal cells (PCs) and especially of broncho-alveolar cells (BACs) with markedly enhanced effector function (killing ability against S. aureus). Generally, Lentinan, known usually with its parenteral routes of application, can be successful to stimulate the host cell response in the respiratory tract by intranasal route of administration.

The Yersinia Ysc-Yop 'type III' weaponry

'Type III secretion'--the mechanism by which some pathogenic bacteria inject proteins straight into the cytosol of eukaryotic cells to 'anaesthetize' or 'enslave' them--was discovered in 1994. Important progress has been made in this area during the past few years: the bacterial organelles responsible for this secretion--called 'injectisomes'--have been visualized, the structures of some of the bacterial protein 'effectors' have been determined, and considerable progress has been made in understanding the intracellular action of the effectors. Type III secretion is key to the pathogenesis of bacteria from the Yersinia genus.

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.

Role of Yops and adhesins in resistance of Yersinia enterocolitica to phagocytosis

Yersinia enterocolitica is a pathogen endowed with two adhesins, Inv and YadA, and with the Ysc type III secretion system, which allows extracellular adherent bacteria to inject Yop effectors into the cytosol of animal target cells. We tested the influence of all of these virulence determinants on opsonic and nonopsonic phagocytosis by PU5-1.8 and J774 mouse macrophages, as well as by human polymorphonuclear leukocytes (PMNs). The adhesins contributed to phagocytosis in the absence of opsonins but not in the presence of opsonins. In agreement with previous results, YadA counteracted opsonization. In every instance, the Ysc-Yop system conferred a significant level of resistance to phagocytosis. Nonopsonized single-mutant bacteria lacking either YopE, -H, -T, or -O were phagocytosed significantly more by J774 cells and by PMNs. Opsonized bacteria were phagocytosed more than nonopsonized bacteria, and mutant bacteria lacking either YopH, -T, or -O were phagocytosed significantly more by J774 cells and by PMNs than were wild-type (WT) bacteria. Opsonized mutants lacking only YopE were phagocytosed significantly more than were WT bacteria by PMNs but not by J774 cells. Thus, YopH, -T, and -O were involved in all of the phagocytic processes studied here but YopE did not play a clear role in guarding against opsonic phagocytosis by J774. Mutants lacking YopP and YopM were, in every instance, as resistant as WT bacteria. Overexpression of YopE, -H, -T, or -O alone did not confer resistance to phagocytosis, although it affected the cytoskeleton. These results show that YopH, YopT, YopO, and, in some instances, YopE act synergistically to increase the resistance of Y. enterocolitica to phagocytosis by macrophages and PMNs.

Resistance to phagocytosis by Yersinia

Enteropathogenic species of the genus Yersinia penetrate the intestinal epithelium and then spread to the lymphatic system, where they proliferate extracellularly. At this location, most other bacteria are effectively ingested and destroyed by the resident phagocytes. Yersinia, on the other hand binds to receptors on the external surface of phagocytes, and from this location it blocks the capacity of these cells to exert their phagocytic function via different receptors. The mechanism behind the resistance to phagocytosis involves the essential virulence factor YopH, a protein tyrosine phosphatase that is translocated into interacting target cells via a type III secretion machinery. YopH disrupts peripheral focal complexes of host cells, seen as a rounding up of infected cells. The focal complex proteins that are dephosphorylated by YopH are focal adhesion kinase and Crk-associated substrate, the latter of which is a common substrate in both professional and non-professional phagocytes. In macrophages additional substrates have been found, the Fyn-binding/SLP-76-associated protein and SKAP-HOM. Phagocytosis is a rapid process that is activated when the bacterium interacts with the phagocyte. Consequently, the effect exerted by a microbe to block this process has to be rapid and precise. This review deals with the mechanisms involved in impeding uptake as well as with the role of the YopH substrates and focal complex structures in normal cell function.

Helicobacter pylori inhibits phagocytosis by professional phagocytes involving type IV secretion components

Gastric infections by Helicobacter pylori are characteristically associated with an intense inflammation and infiltration of mainly polymorphonuclear lymphocytes (PMNs) and monocytes. The inflammatory response by infiltrated immune cells appears to be a primary cause of the damage to surface epithelial layers and may eventually result in gastritis, peptic ulcer, gastric cancer and/or MALT-associated gastric lymphoma. Our analysis of the interaction between H. pylori and PMNs and monocytes revealed that H. pylori inhibits its own uptake by these professional phagocytes. To some degree, this effect resembles antiphagocytosis by Yersinia enterocolitica. Increasing numbers of bacteria associated per cell are more efficient at blocking their own engulfment. In H. pylori, bacterial protein synthesis is necessary to block phagocytic uptake, as shown by the time and concentration dependence of the bacteriostatic protein synthesis inhibitor chloramphenicol. Furthermore, H. pylori appears broadly to inhibit the phagocytic function of monocytes and PMNs, as infection with H. pylori abrogates the phagocytes' ability to engulf latex beads or adherent Neisseria gonorrhoeae cells. This antiphagocytic phenotype depends on distinct virulence (vir) genes, such as virB7 and virB11, encoding core components of a putative type IV secretion apparatus. Our data indicate that H. pylori exhibits an antiphagocytic activity that may play an essential role in the immune escape of this persistent pathogen.

Studies on the interactions of immunostimulated macrophages andYersinia enterocoliticaO:8

Immunological and electron microscopy investigations of the phagocytic and killing activities of peritoneal macrophages from rats and mice against Yersinia enterocolitica serotype O:8 cells were performed. The effect of in vivo application of cytoplasmic membranes (CM) from the stable Escherichia coli WF+ L-form on macrophage activity was also studied. It was established that rat macrophages more actively phagocytosed the plasmidless pYV(-) Y. enterocolitica cells, compared to the plasmid-bearing pYV(+) Y. enterocolitica cells. The killing ability against both variants of the Y. enterocolitica strain was significantly enhanced in macrophages from CM-treated rats after 2 h, 4 h, and 24 h incubation. The CM treatment enhanced the phagocytic activity of the macrophages. The in vitro interaction of normal and immunostimulated rat macrophages with both pYV(+) and pYV(-) variants of Y. enterocolitica did not lead to any additional apoptotic and necrotic changes in macrophages compared to control macrophages, which were cultivated without Y. enterocolitica. Electron-microscopic investigation showed that mouse macrophages eliminated Y. enterocolitica pYV(+) cells in vivo after 24 h. No engulfed or digested bacterial cells were observed. Activation of cell surfaces and vacuolization of macrophage cytoplasm, both of CM-treated non-infected and infected mice, were observed. The experimental results showed that Y. enterocolitica pYV(+) cells could be eliminated by peritoneal macrophages.Key words: Yersinia enterocolitica, immunostimulation, electron microscopy, bacterial L-forms, macrophages.

LcrV of Yersinia pestis enters infected eukaryotic cells by a virulence plasmid-independent mechanism

Yersinia pestis is the causative agent of bubonic plague and possesses a set of plasmid-encoded, secretable virulence proteins termed LcrV and Yops which are essential for survival in mammalian hosts. Yops and LcrV are secreted by a type III mechanism (Ysc), and Yops are unidirectionally targeted into the cytosol of associated eukaryotic cells in a tissue culture infection model. LcrV is required for Yops targeting, and recent findings have revealed that it can localize to the bacterial surface; however, its fate in this infection model has not been investigated in detail. In this study, we compared the localization of LcrV to that of the targeted proteins YopE and YopM by immunoblot analysis of fractions of Yersinia-infected HeLa cultures or by laser-scanning confocal microscopy of infected monolayers. Both LcrV and YopE were secreted by contact-activated, extracellularly localized yersiniae and were targeted to the HeLa cell cytosol. Although a significant amount of LcrV partitioned to the culture medium (unlike YopE), this extracellular pool of LcrV was not the source of the LcrV that entered HeLa cells. Unlike targeting of YopE and YopM, targeting of LcrV occurred in the absence of a functional Ysc apparatus and other virulence plasmid (pCD1)-expressed proteins. However, the Ysc is necessary for LcrV to be released into the medium, and our recent work has shown that localization of LcrV on the bacterial surface requires the Ysc. These results indicate that two mechanisms exist for the secretion of LcrV by Y. pestis, both of which are activated by contact with eukaryotic cells. LcrV secreted by the Ysc reaches the bacterial surface and the surrounding medium, whereas the second is a novel, Ysc-independent pathway which results in localization of LcrV in the cytosol of infected cells but not the surrounding medium.

Characterization of the interaction between Yersinia enterocolitica biotype 1A and phagocytes and epithelial cells in vitro

Yersinia enterocolitica strains of biotype 1A are increasingly being recognized as etiological agents of gastroenteritis. However, the mechanisms by which these bacteria cause disease differ from those of highly invasive, virulence plasmid-bearing Y. enterocolitica strains and are poorly understood. We have investigated several biotype 1A strains of diverse origin for their ability to resist killing by professional phagocytes. All strains were rapidly killed by polymorphonuclear leukocytes but persisted within macrophages (activated with gamma interferon) to a significantly greater extent (survival = 40.5% +/- 17.4%) than did Escherichia coli HB101 (9.3% +/- 0.7%; P = 0.0001). Strains isolated from symptomatic patients were significantly more resistant to killing by macrophages (survival = 48.9% +/- 19.5%) than were strains obtained from food or the environment (survival = 32.1% +/- 10.3%; P = 0.04). Some strains which had been ingested by macrophages or HEp-2 epithelial cells showed a tendency to reemerge into the tissue culture medium over a period lasting several hours. This phenomenon, which we termed "escape," was observed in 14 of 15 strains of clinical origin but in only 3 of 12 nonclinical isolates (P = 0.001). The capacity of bacteria to escape from cells was not directly related to their invasive ability. To determine if escape was due to host cell lysis, we used a variety of techniques, including lactate dehydrogenase release, trypan blue exclusion, and examination of infected cells by light and electron microscopy, to measure cell viability and lysis. These studies established that biotype 1A Y. enterocolitica strains were able to escape from macrophages or epithelial cells without causing detectable cytolysis, suggesting that escape was achieved by a process resembling exocytosis. The observations that biotype 1A Y. enterocolitica strains of clinical origin are significantly more resistant to killing by macrophages and significantly more likely to escape from host cells than are strains of nonclinical origin suggest that these properties may account for the virulence of these bacteria.

Yersinia pseudotuberculosis-induced calcium signaling in neutrophils is blocked by the virulence effector YopH

Pathogenic species of the genus Yersinia evade the bactericidal functions of phagocytes. This evasion is mediated through their virulence effectors, Yops, which act within target cells. In this study we investigated the effect of Yersinia pseudotuberculosis on Ca2+ signaling in polymorphonuclear neutrophils. The intracellular free calcium concentration in single adherent human neutrophils was monitored during bacterial infection and, in parallel, the encounter between the bacteria and cells was observed. When a plasmid-cured strain was used for infection, adherence of a single bacterium to the cellular surface induced a beta1 integrin-dependent transient increase in the intracellular concentration of free calcium. This was, however, not seen with Yop-expressing wild-type bacteria, which adhered to the cell surface without generating any Ca2+ signal. Importantly, the overall Ca2+ homeostasis was not affected by the wild-type strain; the Ca2+ signal mediated by the G-protein-coupled formyl-methionyl-leucyl-phenylalanine receptor was still functioning. Hence, the blocking effect was restricted to certain receptors and their signaling pathways. The use of different Yop mutant strains revealed that the protein tyrosine phosphatase YopH was responsible for the inhibition. This virulence determinant has previously been implicated in very rapid Yersinia-mediated effects on target cells as the key effector in the blockage of phagocytic uptake. The present finding, that Y. pseudotuberculosis, via YopH, specifically inhibits a self-induced immediate-early Ca2+ signal in neutrophils, offers more-detailed information concerning the effectiveness of this virulence effector and implies an effect on Ca2+-dependent, downstream signals.

Yops of Yersinia enterocolitica inhibit receptor-dependent superoxide anion production by human granulocytes

The virulence plasmid-borne genes encoding Yersinia adhesin A (YadA) and several Yersinia secreted proteins (Yops) are involved in the inhibition of phagocytosis and killing of Yersinia enterocolitica by human granulocytes. One of these Yops, YopH, dephosphorylates multiple tyrosine-phosphorylated proteins in eukaryotic cells and is involved in the inhibition of phagocytosis of Y. enterocolitica by human granulocytes. We investigated whether antibody- and complement-opsonized plasmid-bearing (pYV+) Y. enterocolitica inhibits O2- production by human granulocytes in response to various stimuli and whether YopH is involved. Granulocytes were preincubated with mutant strains unable to express YadA or to secrete Yops or YopH. O2- production by granulocytes during stimulation was assessed by measuring the reduction of ferricytochrome c. PYV+ Y. enterocolitica inhibited O2- production by granulocytes incubated with opsonized Y. enterocolitica or N-formyl-Met-Leu-Phe (f-MLP). This inhibitory effect mediated by pYV did not affect receptor-independent O2- production by granulocytes in response to phorbol myristate acetate, indicating that NADPH activity remained unaffected after activation of protein kinase C. The inhibition of f-MLP-induced O2- production by granulocytes depends on the secretion of Yops and not on the expression of YadA. Insertional inactivation of the yopH gene abrogated the inhibition of phagocytosis of antibody- and complement-opsonized Y. enterocolitica by human granulocytes but not of the f-MLP-induced O2- production by granulocytes or tyrosine phosphorylation of granulocyte proteins. These findings suggest that the specific targets for YopH are not present in f-MLP receptor-linked signal transduction and that other Yop-mediated mechanisms are involved.

The virulence plasmid of Yersinia, an antihost genome

The 70-kb virulence plasmid enables Yersinia spp. (Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica) to survive and multiply in the lymphoid tissues of their host. It encodes the Yop virulon, an integrated system allowing extracellular bacteria to disarm the cells involved in the immune response, to disrupt their communications, or even to induce their apoptosis by the injection of bacterial effector proteins. This system consists of the Yop proteins and their dedicated type III secretion apparatus, called Ysc. The Ysc apparatus is composed of some 25 proteins including a secretin. Most of the Yops fall into two groups. Some of them are the intracellular effectors (YopE, YopH, YpkA/YopO, YopP/YopJ, YopM, and YopT), while the others (YopB, YopD, and LcrV) form the translocation apparatus that is deployed at the bacterial surface to deliver the effectors into the eukaryotic cells, across their plasma membrane. Yop secretion is triggered by contact with eukaryotic cells and controlled by proteins of the virulon including YopN, TyeA, and LcrG, which are thought to form a plug complex closing the bacterial secretion channel. The proper operation of the system also requires small individual chaperones, called the Syc proteins, in the bacterial cytosol. Transcription of the genes is controlled both by temperature and by the activity of the secretion apparatus. The virulence plasmid of Y. enterocolitica and Y. pseudotuberculosis also encodes the adhesin YadA. The virulence plasmid contains some evolutionary remnants including, in Y. enterocolitica, an operon encoding resistance to arsenic compounds.

YopH of Yersinia pseudotuberculosis interrupts early phosphotyrosine signalling associated with phagocytosis

The PTPase YopH of Yersinia is essential to the ability of these bacteria to block phagocytosis. Wild-type Yersinia pseudotuberculosis, but not the yopH mutant strain, resisted phagocytosis by J774 cells. Ingestion of a yopH mutant was dependent on tyrosine kinase activity. Transcomplementation with wild-type yopH restored the anti-phagocytic effect, whereas introduction of the gene encoding the catalytically inactive yopHC403A was without effect. The PTPase inhibitor orthovanadate impaired the anti-phagocytic effect of the wild-type strain, further demonstrating the importance of bacteria-derived PTPase activity for this event. The ability to resist phagocytosis indicates that the effect of the bacterium is immediately exerted when it becomes associated with the phagocyte. Within 30 s after the onset of infection, wild-type Y. pseudotuberculosis caused a YopH-dependent dephosphorylation of phosphotyrosine proteins in J774 cells. Furthermore, interaction of the cells with phagocytosable strains led to a rapid and transient increase in tyrosine phosphorylation of paxillin and some other proteins, an event dependent on the presence of the bacterial surface-located protein invasin. Co-infection with the phagocytosable strain and the wild-type strain abolished the induction of tyrosine phosphorylation. Taken together, the present findings demonstrate an immediate YopH-mediated dephosphorylation of macrophage phosphotyrosine proteins, suggesting that this PTPase acts by preventing early phagocytosis-linked signalling in the phagocyte.

Role of YadA in resistance to killing of Yersinia enterocolitica by antimicrobial polypeptides of human granulocytes

The virulence plasmid pYVe of Yersinia enterocolitica codes for the production of the outer membrane protein YadA and the secretion of several proteins, called Yops, which may protect this bacterium against killing by human granulocytes. Granulocytes kill ingested microorganisms by oxygen-dependent and oxygen-independent mechanisms, the latter including antimicrobial polypeptides. The aim of this study was to determine whether virulent (pYVe+) Y. enterocolitica and plasmid-cured avirulent (pYVe-) Y. enterocolitica differ in susceptibility to antimicrobial polypeptides extracted from granules of human granulocytes. The acetic acid granule extract contained several polypeptides with antimicrobial activity against Y. enterocolitica as determined by gel overlay and radial diffusion assays. Two of these polypeptides were identified as lysozyme and defensins. pYVe+ Y. enterocolitica was less susceptible than pYVe- Y. enterocolitica to the antimicrobial activity of granule extract, lysozyme, and defensins as determined in a suspension assay, which indicated that the pYVe plasmid mediates a reduced susceptibility to these polypeptides. The role of YadA in the resistance to antimicrobial polypeptides was analyzed by using mutants of Y. enterocolitica that specifically lack or express YadA. The results demonstrated that YadA conferred resistance to the killing of Y. enterocolitica by the granule extract. Together, these results indicate that the plasmid-encoded factor YadA contributes to the resistance of Y. enterocolitica to the killing by antimicrobial polypeptides of human granulocytes.

Differential contribution of Yersinia enterocolitica virulence factors to evasion of microbicidal action of neutrophils

The differential contribution of the virulence factors invasin, protein tyrosine phosphatase (YopH), cytotoxin (YopE), and adhesin (YadA) of Yersinia enterocolitica to evasion of the antibacterial activities of polymorphonuclear leukocytes (PMNs) (oxidative burst, phagocytosis, killing) was analyzed. We constructed virulence gene knockout mutants and a novel two-plasmid system allowing production and secretion of individual virulence factors. Wild-type Y. enterocolitica WA-314 harboring the virulence plasmid pYV08 resisted phagocytosis and killing by PMNs. Moreover, strain WA-314 was able to inhibit the neutrophil oxidative burst upon stimulation with opsonized zymosan independently on preincubation with normal human serum or YadA-specific serum. These phenotypic properties of strain WA-314 were differentially affected when mutants impaired in YadA production or Yop secretion were used. A more detailed analysis revealed that YopH plays the dominant role in suppression of the antibacterial action of PMNs without damaging the cells. The YopH suppressing effect could be enhanced by coproduction of YopE and YadA. The contribution of YadA is attributed to the adhesin function promoting interaction with PMNs under both opsonizing and nonopsonizing conditions. In contrast, invasin seems to mediate only opsonin-independent interaction with PMNs. Taken together, our results demonstrate that YopH, YopE, and YadA act in concert towards neutrophil attack to enable extracellular survival of Y. enterocolitica in host tissue.