Yops of Yersinia spp. pathogenic for humans

Seroepidemiological survey of pathogenic Yersinia in domestic pigs in Chiba Prefecture, Japan

This study aimed to investigate the prevalence of antibodies against pathogenic Yersinia such as Y. enterocolitica and Y. pseudotuberculosis in domestic pigs. A total of 650 serum samples from pigs in nine regions of the Chiba Prefecture in Japan, were tested using plasmid-encoded Yersinia outer membrane protein (Yops) antigen ELISA. The cutoff value was calculated using 20 pathogenic Yersinia-free pig serum samples. According to the cutoff value, 246 (37.8%) pigs from seven regions were considered seropositive for pathogenic Yersinia during the study period. These results indicate that pathogenic Yersinia is widespread in pigs in Chiba, which may become the source of human yersiniosis in this region.

The Natural and Clinical History of Plague: From the Ancient Pandemics to Modern Insights

The human pathogen Yersinia pestis is responsible for bubonic, septicemic, and pneumonic plague. A deeply comprehensive overview of its historical context, bacteriological characteristics, genomic analysis based on ancient DNA (aDNA) and modern strains, and its impact on historical and actual human populations, is explored. The results from multiple studies have been synthesized to investigate the origins of plague, its transmission, and effects on different populations. Additionally, molecular interactions of Y. pestis, from its evolutionary origins to its adaptation to flea-born transmission, and its impact on human and wild populations are considered. The characteristic combinations of aDNA patterns, which plays a decisive role in the reconstruction and analysis of ancient genomes, are reviewed. Bioinformatics is fundamental in identifying specific Y. pestis lineages, and automated pipelines are among the valuable tools in implementing such studies. Plague, which remains among human history's most lethal infectious diseases, but also other zoonotic diseases, requires the continuous investigation of plague topics. This can be achieved by improving molecular and genetic screening of animal populations, identifying ecological and social determinants of outbreaks, increasing interdisciplinary collaborations among scientists and public healthcare providers, and continued research into the characterization, diagnosis, and treatment of these diseases.

Type 3 secretion system induced leukotriene B4 synthesis by leukocytes is actively inhibited by Yersinia pestis to evade early immune recognition

Subverting the host immune response to inhibit inflammation is a key virulence strategy of Yersinia pestis. The inflammatory cascade is tightly controlled via the sequential action of lipid and protein mediators of inflammation. Because delayed inflammation is essential for Y. pestis to cause lethal infection, defining the Y. pestis mechanisms to manipulate the inflammatory cascade is necessary to understand this pathogen's virulence. While previous studies have established that Y. pestis actively inhibits the expression of host proteins that mediate inflammation, there is currently a gap in our understanding of the inflammatory lipid mediator response during plague. Here we used the murine model to define the kinetics of the synthesis of leukotriene B4 (LTB4), a pro-inflammatory lipid chemoattractant and immune cell activator, within the lungs during pneumonic plague. Furthermore, we demonstrated that exogenous administration of LTB4 prior to infection limited bacterial proliferation, suggesting that the absence of LTB4 synthesis during plague contributes to Y. pestis immune evasion. Using primary leukocytes from mice and humans further revealed that Y. pestis actively inhibits the synthesis of LTB4. Finally, using Y. pestis mutants in the Ysc type 3 secretion system (T3SS) and Yersinia outer protein (Yop) effectors, we demonstrate that leukocytes recognize the T3SS to initiate the rapid synthesis of LTB4. However, several Yop effectors secreted through the T3SS effectively inhibit this host response. Together, these data demonstrate that Y. pestis actively inhibits the synthesis of the inflammatory lipid LTB4 contributing to the delay in the inflammatory cascade required for rapid recruitment of leukocytes to sites of infection.

The Use of an Organo-Selenium Peptide to Develop New Antimicrobials That Target a Specific Bacteria

This study examines the use of a covalently selenium-bonded peptide and phage that binds to the Yersinia pestis F1 antigen for the targeting and killing of E. coli expressing this surface antigen. Using a Ph.D.-12 phage-display library for affinity selection of the phage which would bind the F1 antigen of Y. pestis, a phage displaying a peptide that binds the F1 antigen with high affinity and specificity was identified. Selenium was then covalently attached to the display phage and the corresponding F1-antigen-binding peptide. Both the phage and peptides with selenium covalently attached retained their binding specificity for the Y. pestis F1 antigen. The phage or peptide not labeled with selenium did not kill the targeted bacteria, while the phage or peptide labeled with selenium did. In addition, the seleno-peptide, expressing the F1 targeting sequence only, killed cells expressing the F1 antigen but not the parent strain that did not express the F1 antigen. Specifically, the seleno-peptide could kill eight logs of bacteria in less than two hours at a 10-µM concentration. These results demonstrate a novel approach for the development of an antibacterial agent that can target a specific bacterial pathogen for destruction through the use of covalently attached selenium and will not affect other bacteria.

Zoonotic Infections and Biowarfare Agents in Critical Care: Anthrax, Plague, and Tularemia

Bacterial zoonotic infections are rare in developed countries in the twenty-first century but may cause major morbidity and mortality in developing regions of the world. In addition, their potential use as biological weapons makes early recognition and effective empiric therapy important for the critical care practitioner. Anthrax, plague, and tularemia share overlapping presenting syndromes, including fulminant respiratory infections and less severe but still highly morbid lymphocutaneous infections. Although all three may be transmitted as infectious aerosols, only plague has a risk of direct human-to-human transmission. Diagnostic testing will require special precautions for laboratory staff and most often involvement of regional and national reference laboratories. Empiric therapy with aminoglycosides may be life-saving for plague and tularemia, while the treatment of anthrax is complex and varies depending on the site of infection. In outbreaks or for post-exposure prophylaxis, treatment with doxycycline or a fluoroquinolone is recommended for all three diseases.

Lipopolysaccharide-associated resistance to killing of yersiniae by complement

Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica share ~70 kb low calcium response (Lcr) plasmids encoding virulence factors expressed at 37°C that, except for the adhesin YadA, are repressed by Ca2+(Lcr+). Virulence factors encoded on both the Lcr plasmid and chromosome have been reported to protect yersiniae against complement-dependent killing. In this study, LPS was isolated from yersiniae of serum-sensitive phenotypes (Lcr+and Lcr-Y. enterocolitica and Y. pseudotuberculosis grown at 26°C and Lcr-Y. enterocolitica grown at 37°C) and incorporated into liposomes containing radioactive chromium. These vesicles lysed with release of free51Cr in normal but not decomplemented serum. Liposomes prepared from serum-resistant phenotypes (Lcr+and Lcr-Y. pestis grown at 26°C or 37°C, Lcr+and Lcr-Y. pseudotubercu losis grown at 37°C, and Lcr+Y. enterocolitica grown at 37°C) did not undergo complement-dependent lysis. LPS from serum-resistant Y. pestis and Y. pseudotuberculosis was rough as judged by deficiency of O-groups.

Immunogenicity and safety of subunit plague vaccine: A randomized phase 2a clinical trial

BACKGROUND

Although the killed whole-cell and live attenuated plague vaccine have been licensed, they are rarely used today because of toxicities, limited evidence of efficacy against plague, poor immune persistence required booster immunization every year, and limited commercial availability. This study was a randomized phase 2a clinical trial aimed to evaluating the immunogenicity and safety of a novel subunit plague vaccine.

METHODS

240 healthy adults aged 18-55 y were enrolled and randomly assigned at a ratio of 1:1 to receive 2 doses of 15 or 30 mcg vaccine at a 28-day interval between doses. Blood samples were collected at day 0, 28 and 56. Adverse events were collected during the first 28 d after each vaccination. Serious Adverse Event was observed throughout the study period.

RESULTS

239 participants received the first dose at day 0 and 238 received the second dose at day 28. Antibodies to envelope antigen faction 1 (F1) and recombinant virulence antigen (rV) were increased at day 28, and boosted significantly at day 56. For anti-F1 antibodies, geometric mean titer (GMT) and geometric mean fold increase (GMFI) were significantly higher in 30 mcg group than in the 15 mcg group(each P1< 0.05 at day 28 and each P1< 0.001 at day 56), with similar seroconversion rate of antibodies between 15 and 30 mcg group at both of the 2 time points. For anti-rV antibodies, seroconversion rate at day 28 in 30 mcg group was higher than that in 15 mcg group. However, GMT and GMFI of anti-rV antibodies were increased to approximately the same levels in the 2 groups. Similar booster immune response was also noticed in both groups at day 56. The injections were well tolerated, with mainly mild or moderate local and systemic adverse reactions (lower than grad 3). The proportion of pain at injection site was higher in 30 mcg group. None of SAEs were reported during 56 d.

CONCLUSION

The plague vaccine comprised of F1 and rV antigens showed good safety and immunogenicity in adults aged 18-55 y old. The data show that the 30 mcg formulation is generally more immunogenic than the 15 mcg formulation, and represents the preferred formulation for further clinical development. It will be important to evaluate the long-term efficacy for appropriate formulations of the plague subunit vaccine.

Plant Pathogenic Microbial Communication Affected by Elevated Temperature in Pectobacterium carotovorum subsp. carotovorum

Gram-negative plant pathogenic bacteria regulate specific gene expression in a population density-dependent manner by sensing level of Acyl-Homoserine Lactone (HSL) molecules which they produce and liberate to the environment, called Quorum Sensing (QS). The production of virulence factors (extracellular enzyme viz. cellulase, pectinase, etc.) in Pectobacterium carotovorum subsp. carotovorum (Pcc) is under strong regulation of QS. The QS signal molecule, N-(3-oxohexanoyl)-L-Homoserine Lactone (OHHL) was found as the central regulatory system for the virulence factor production in Pcc and is also under strict regulation of external environmental temperature. Under seven different incubation temperatures (24, 26, 28, 30, 33, 35, and 37 °C) in laboratory condition, highest amount of OHHL (804 violacein unit) and highest (79 %) Disease Severity Index (DSI) were measured at 33 °C. The OHHL production kinetics showed accumulation of highest concentration of OHHL at late log phase of the growth but diminution in the concentration occurred during stationary phase onwards to death phase. At higher temperature (35 and 37 °C) exposure, OHHL was not at detectable range. The effect of temperature on virulence factor production is the concomitant effect of HSL production and degradation which justifies less disease severity index in cross-inoculated tomato fruits incubated at 35 and 37 °C. The nondetection of the OHHL in the elevated temperature may because of degradation as these signal molecules are quite sensitive and prone to get degraded under different physical factors. This result provides the rationale behind the highest disease severity up to certain elevated temperature and leaves opportunities for investigation on mutation, co-evolution of superior plant pathogen with more stable HSL signals-mediated pathogenesis under global warming context.

Preclinical Safety Assessment of a Recombinant Plague Vaccine (rF1V)

A recombinant vaccine (rF1V) is being developed to protect adults 18 to 55 years of age from fatal pneumonic plague caused by aerosolized Yersinia pestis. A comprehensive series of studies was conducted to evaluate the general toxicity and local reactogenicity of the rF1V vaccine prior to first use in humans. Toxicity was evaluated in CD-1 mice vaccinated with control material and three dosage concentrations of rF1V with or without Alhydrogel® by intramuscular (IM) injection on Study Days 1, 29, 57 and 71 in a volume of 0.1 mL. Total immunizing protein given in each dose was 0, 20 or 60 μg/animal. Local reactogenicity was evaluated in mice at the dosages given and in New Zealand white (NZW) rabbits using the same injection volume and formulations (40, 80, 160 and 320 μg/mL total antigen and 0.3% (w/v) Alhydrogel®) intended for human use (0.5 mL). The rF1V vaccine produced no apparent systemic toxicity and only transient edema and erythema at the injection site. Together these results indicated a favorable safety profile for rF1V and supported its use in a Phase 1 clinical trial.

Establishment of a Swiss Webster mouse model of pneumonic plague to meet essential data elements under the animal rule

A recombinant vaccine (rF1V) is being developed for protection against pneumonic plague. This study was performed to address essential data elements to establish a well-characterized Swiss Webster mouse model for licensing the rF1V vaccine using the FDA's Animal Rule. These elements include the documentation of challenge material characteristics, aerosol exposure parameters, details of the onset and severity of clinical signs, pathophysiological response to disease, and relevance to human disease. Prior to animal exposures, an evaluation of the aerosol system was performed to determine and understand the variability of the aerosol exposure system. Standardized procedures for the preparation of Yersinia pestis challenge material also were developed. The 50% lethal dose (LD(50)) was estimated to be 1,966 CFU using Probit analysis. Following the LD(50) determination, pathology was evaluated by exposing mice to a target LD(99) (42,890 CFU). Mice were euthanized at 12, 24, 36, 48, 60, and 72 h postexposure. At each time point, samples were collected for clinical pathology, detection of bacteria in blood and tissues, and pathology evaluations. A general increase in incidence and severity of microscopic findings was observed in the lung, lymph nodes, spleen, and liver from 36 to 72 h postchallenge. Similarly, the incidence and severity of pneumonia increased throughout the study; however, some mice died in the absence of pneumonia, suggesting that disease progression does not require the development of pneumonia. Disease pathology in the Swiss Webster mouse is similar to that observed in humans, demonstrating the utility of this pneumonic plague model that can be used by researchers investigating plague countermeasures.

Concerted actions of a thermo-labile regulator and a unique intergenic RNA thermosensor control Yersinia virulence

Expression of all Yersinia pathogenicity factors encoded on the virulence plasmid, including the yop effector and the ysc type III secretion genes, is controlled by the transcriptional activator LcrF in response to temperature. Here, we show that a protein- and RNA-dependent hierarchy of thermosensors induce LcrF synthesis at body temperature. Thermally regulated transcription of lcrF is modest and mediated by the thermo-sensitive modulator YmoA, which represses transcription from a single promoter located far upstream of the yscW-lcrF operon at moderate temperatures. The transcriptional response is complemented by a second layer of temperature-control induced by a unique cis-acting RNA element located within the intergenic region of the yscW-lcrF transcript. Structure probing demonstrated that this region forms a secondary structure composed of two stemloops at 25°C. The second hairpin sequesters the lcrF ribosomal binding site by a stretch of four uracils. Opening of this structure was favored at 37°C and permitted ribosome binding at host body temperature. Our study further provides experimental evidence for the biological relevance of an RNA thermometer in an animal model. Following oral infections in mice, we found that two different Y. pseudotuberculosis patient isolates expressing a stabilized thermometer variant were strongly reduced in their ability to disseminate into the Peyer's patches, liver and spleen and have fully lost their lethality. Intriguingly, Yersinia strains with a destabilized version of the thermosensor were attenuated or exhibited a similar, but not a higher mortality. This illustrates that the RNA thermometer is the decisive control element providing just the appropriate amounts of LcrF protein for optimal infection efficiency.

Virulence Plasmid (pYV)-Associated Expression of Phenotypic Virulent Determinants in Pathogenic Yersinia Species: A Convenient Method for Monitoring the Presence of pYV under Culture Conditions and Its Application for Isolation/Detection of Yersinia pestis in Food

In Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica, phenotypic expression of virulence plasmid (pYV: 70-kb)-associated genetic determinants may include low-calcium response (Lcr, pinpoint colony, size = 0.36 mm), colony morphology (size = 1.13 mm), crystal violet (CV) binding (dark-violet colony), Congo Red (CR) uptake (red pinpoint colony, size = 0.36 mm), autoagglutination (AA = cells agglutinate), and hydrophobicity (HP = clumping of cells). Y. pseudotuberculosis is chromosomally closely related to Y. pestis; whereas, Y. enterocolitica is chromosomally more distantly related to Y. pestis and Y. pseudotuberculosis. All three species demonstrate Lcr, CV binding, and CR uptake. The colony morphology/size, AA, and HP characteristics are expressed in both Y. pseudotuberculosis and Y. enterocolitica but not in Y. pestis. Congo red uptake in Y. pestis was demonstrated only on calcium-deficient CR magnesium oxalate tryptic soy agar (CR-MOX), whereas this phenotype was expressed on both CR-MOX and low-calcium agarose media in Y. pseudotuberculosis and Y. enterocolitica. These phenotypes were detectable at 37°C within 24 h in Y. enterocolitica and Y. pseudotuberculosis but did not appear until 48 h in Y. pestis due to its slower growth rate at 37°C. The pYV is unstable (i.e., easily lost under a variety of culture conditions) in all three species but is more unstable in Y. pestis. The specific CR uptake by Y. pestis in CR-MOX and the delayed time interval to express Lcr and CR uptake provide a means to differentiate Y. pestis from Y. enterocolitica and Y. pseudotuberculosis. These differences in pYV expression in Y. pestis can be used for its isolation and detection in food.

A procedure for monitoring the presence of the virulence plasmid (pYV) in Yersinia pestis under culture conditions

The pathogenicity of Yersinia pestis depends on the presence of a virulence plasmid (pYV). The unstable nature of pYV in Y. pestis leads to the eventual outgrowth of pYV-less cells due to its higher growth rate. Thus, it was necessary to develop procedures to monitor the presence of the plasmid during cultivation, storage, and laboratory manipulations. A procedure was developed to monitor the presence of pYV in Y. pestis by using low calcium response and Congo red binding techniques. The selection of pYV in the isolated clones was confirmed by polymerase chain reaction and by expression of pYV-associated phenotypes. Thus, using this procedure, low calcium response-Congo red-positive clones can be isolated for use in the development of growth models of virulent Y. pestis in food.

Seroepidemiological survey of pathogenic Yersinia in breeding squirrel monkeys in Japan

To investigate the prevalence of antibodies to pathogenic Yersinia in breeding squirrel monkeys, the serum samples of 252 squirrel monkeys from 9 zoological gardens in Japan were tested by ELISA using plasmid-encoded Yersinia outer membrane protein (Yops) as the antigen. The cutoff value was calculated by using the serum samples of the squirrel monkeys from Suriname, where no prevalence of pathogenic Yersinia have been reported. According to the cutoff value, 164 of 252 (65.1%) squirrel monkeys were considered positive against pathogenic Yersinia. These positive monkeys belonged to 8 of the 9 zoological gardens, and the percentage of the seropositive monkeys ranged from 22.2 to 89.4%. Furthermore, in one zoological garden, the positive rate of the squirrel monkeys which were over 1 year old (95.7%) was significantly higher than those which were under 1 year old (23.3%). These results suggested that pathogenic Yersinia is highly prevalent among breeding monkeys in Japan.

Inactivation of the fliY gene encoding a flagellar motor switch protein attenuates mobility and virulence of Leptospira interrogans strain Lai

Background

Pathogenic Leptospira species cause leptospirosis, a zoonotic disease of global importance. The spirochete displays active rotative mobility which may contribute to invasion and diffusion of the pathogen in hosts. FliY is a flagellar motor switch protein that controls flagellar motor direction in other microbes, but its role in Leptospira, and paricularly in pathogenicity remains unknown.

Results

A suicide plasmid for the fliY gene of Leptospira interrogans serogroup Icterohaemorrhagiae serovar Lai strain Lai that was disrupted by inserting the ampicillin resistance gene (bla) was constructed, and the inactivation of fliY gene in a mutant (fliY^-) was confirmed by PCR and Western Blot analysis. The inactivation resulted in the mRNA absence of fliP and fliQ genes which are located downstream of the fliY gene in the same operon. The mutant displayed visibly weakened rotative motion in liquid medium and its migration on semisolid medium was also markedly attenuated compared to the wild-type strain. Compared to the wild-type strain, the mutant showed much lower levels of adhesion to murine macrophages and apoptosis-inducing ability, and its lethality to guinea pigs was also significantly decreased.

Conclusion

Inactivation of fliY, by the method used in this paper, clearly had polar effects on downstream genes. The phentotypes observed, including lower pathogenicity, could be a consequence of fliY inactivation, but also a consequence of the polar effects.

Further development of raccoon poxvirus-vectored vaccines against plague (Yersinia pestis)

In previous studies, we demonstrated protection against plague in mice and prairie dogs using a raccoon pox (RCN) virus-vectored vaccine that expressed the F1 capsular antigen of Yersinia pestis. In order to improve vaccine efficacy, we have now constructed additional RCN-plague vaccines containing two different forms of the lcrV (V) gene, including full-length (Vfull) and a truncated form (V307). Mouse challenge studies with Y. pestis strain CO92 showed that vaccination with a combination of RCN-F1 and the truncated V construct (RCN-V307) provided the greatest improvement (P=0.01) in protection against plague over vaccination with RCN-F1 alone. This effect was mediated primarily by anti-F1 and anti-V antibodies and both contributed independently to increased survival of vaccinated mice.

Deletion of Braun lipoprotein gene (lpp) attenuates Yersinia pestis KIM/D27 strain: role of Lpp in modulating host immune response, NF-kappaB activation and cell death

The pathogenic species of yersiniae potently blocks immune responses in host cells by using the type III secretion apparatus and its effector proteins. In this study, we characterized potential mechanisms associated with the Braun lipoprotein (Lpp) that contributed to a further attenuation of a pigmentation locus-minus Yersinia pestis KIM/D27 mutant strain and its ability to generate immune responses in mice. The lpp gene encodes one of the major outer membrane lipoproteins that is involved in inflammatory responses and septic shock. We found that sera and splenocytes from Deltalpp mutant-immunized mice, when transferred to naïve animals, provided protection to the latter against challenge with a lethal dose of the Y. pestis parental strain. Further, the Deltalpp mutant promoted ex vivo a significantly higher interleukin (IL)-2 and interferon-gamma production from T cells of immunized mice, when compared to those from animals infected with the sub-lethal dose of the parental Y. pestis KIM/D27 strain. Likewise, murine primary macrophages infected with the mutant, when compared to those infected with the parental strain in vitro, produced significantly higher IL-12 levels. Importantly, increased nuclear factor-kappa B activation and decreased apoptosis were noted in splenocytes and primary macrophages of mice challenged with the Deltalpp mutant, when compared to those in animals infected with the parental Y. pestis KIM/D27 strain. Finally, significantly higher levels of antibodies specific for the parental Y. pestis antigens were developed in mice first immunized with the Deltalpp mutant and then challenged with the parental strain, compared to the antibody levels in animals that were immunized and then infected with the parental KIM/D27 strain. To our knowledge, this is the first report of a mechanistic basis for attenuation and immunological responses associated with deletion of the lpp gene from the Y. pestis KIM/D27 strain.

Modulation of dendritic cell differentiation and function by YopJ ofYersinia pestis

Yersinia pestis evades immune responses in part by injecting into host immune cells several effector proteins called Yersinia outer proteins (Yops) that impair cellular function. This has been best characterized in the innate effector cells, but much less so for cells involved in adaptive immune responses. Dendritic cells (DC) sit at the crossroads between innate and adaptive immunity, and can function to initiate or inhibit adaptive immune responses. Although Y. pestis can target and inactivate DC, the mechanism responsible for this remains unclear. We have found that injection of Y. pestis YopJ into DC progenitors disrupts key signal transduction pathways and interferes with DC differentiation and subsequent function. YopJ injection prevents up-regulation of the NF-kappaB transcription factor Rel B and inhibits MAPK/ERK activation--both having key roles in DC differentiation. Furthermore, YopJ injection prevents costimulatory ligand up-regulation, LPS-induced cytokine expression, and yields differentiated DC with diminished capability to induce T cell proliferation and IFN-gamma induction. By modulating DC function through YopJ-mediated disruption of signaling pathways during progenitor to DC differentiation, Yersinia may interfere with the adaptive responses necessary to clear the infection as well as establish a tolerant immune environment that leads to chronic infection/carrier state in the surviving host.

Early interaction of Yersinia pestis with APCs in the lung

Despite the importance of pneumonic plague, little is known of the early pulmonary immune responses that occur following inhalation of Yersinia pestis. Therefore, we conducted studies to identify the early target cells for uptake of Y. pestis in the lungs following intratracheal or i.v. inoculation. Following intratracheal inoculation, Y. pestis was rapidly internalized primarily by a distinctive population of CD11c+DEC-205+CD11b- cells in the airways, whereas i.v. inoculation resulted in uptake primarily by CD11b+CD11c- macrophages and granulocytes in lung tissues. The airway cells internalized and were infected by Y. pestis, but did not support active replication of the organism. Intratracheal inoculation of Y. pestis resulted in rapid activation of airway CD11c+ cells, followed within 24 h by the selective disappearance of these cells from the airways and lungs and the accumulation of apoptotic CD11c+ cells in draining lymph nodes. When CD11c+ cells in the airways were depleted using liposomal clodronate before infection, this resulted in a significantly increased replication of Y. pestis in the lungs and dissemination to the spleen and draining lymph nodes. These findings suggest that CD11c+ cells in the airways play an important role in suppressing the initial replication and dissemination of inhaled Y. pestis, although these results will also require confirmation using fully virulent strains of Y. pestis. Depletion of these airway cells by Y. pestis may therefore be one strategy the organism uses to overcome pulmonary defenses following inhalation of the organism.

Elevated temperature enhances virulence of Erwinia carotovora subsp. carotovora strain EC153 to plants and stimulates production of the quorum sensing signal, N-acyl homoserine lactone, and extracellular proteins

Erwinia carotovora subsp. atroseptica, E. carotovora subsp. betavasculorum, and E. carotovora subsp. carotovora produce high levels of extracellular enzymes, such as pectate lyase (Pel), polygalacturonase (Peh), cellulase (Cel), and protease (Prt), and the quorum-sensing signal N-acyl-homoserine lactone (AHL) at 28 degrees C. However, the production of these enzymes and AHL by these bacteria is severely inhibited during growth at elevated temperatures (31.2 degrees C for E. carotovora subsp. atroseptica and 34.5 degrees C for E. carotovora subsp. betavasculorum and most E. carotovora subsp. carotovora strains). At elevated temperatures these bacteria produce high levels of RsmA, an RNA binding protein that promotes RNA decay. E. carotovora subsp. carotovora strain EC153 is an exception in that it produces higher levels of Pel, Peh, Cel, and Prt at 34.5 degrees C than at 28 degrees C. EC153 also causes extensive maceration of celery petioles and Chinese cabbage leaves at 34.5 degrees C, which correlates with a higher growth rate and higher levels of rRNA and AHL. The lack of pectinase production by E. carotovora subsp. carotovora strain Ecc71 at 34.5 degrees C limits the growth of this organism in plant tissues and consequently impairs its ability to cause tissue maceration. Comparative studies with ahlI (the gene encoding a putative AHL synthase), pel-1, and peh-1 transcripts documented that at 34.5 degrees C the RNAs are more stable in EC153 than in Ecc71. Our data reveal that overall metabolic activity, AHL levels, and mRNA stability are responsible for the higher levels of extracellular protein production and the enhanced virulence of EC153 at 34.5 degrees C compared to 28 degrees C.

Recombinant fraction 1 protein of Yersinia pestis activates murine peritoneal macrophages in vitro

Fraction 1 antigen of Yersinia pestis is a capsule protein of 17.5kDa, known to induce thymocyte proliferation and have anti-phagocytic role in macrophages. It serves as a major protective antigen against challenge of Y. pestis by inducing high concentration of IgG1 antibody response. In the present investigation it is observed that 10microg/ml of rF1 antigen activated murine peritoneal macrophages in vitro. rF1 induced the production of TNF-alpha, IL-1, IL-6, and NO. rF1 treatment also induced increased transcription of IFN-gamma and its related chemokines KC, IP-10, MIP-1alpha, MIP-1beta, MCP-1, RANTES in macrophages. Significantly increased transcription of TLR5 was observed in macrophages treated with rF1, while the expression of TLR2 and TLR4 remained unaffected.

The plague virulence protein YopM targets the innate immune response by causing a global depletion of NK cells

Yersinia pestis, the etiologic agent of plague, delivers six Yersinia outer proteins (Yops) into host cells upon direct bacterial contact. One of these, YopM, is necessary for virulence in a mouse model of septicemic plague, but its pathogenic function is unknown. We report here the immune processes affected by YopM during infection. To test whether the innate or adaptive immune system is targeted by YopM, C57BL/6 (B6) and B6 SCID mice were infected with either the conditionally virulent Y. pestis KIM5 or a yopM deletion mutant and evaluated for bacterial growth in spleen and liver. Both B6 and SCID mice succumbed to infection with Y. pestis KIM5, whereas both mouse strains survived infection by the YopM(-) mutant. These data showed that YopM counteracts innate defenses present in SCID mice. The YopM(-) strain grew more slowly than the parent Y. pestis during the first 4 days of infection in both mouse strains, indicating an early pathogenic role for YopM. In B6 mice, populations of cells of the immune system were not differentially affected by the two Y. pestis strains, with one major exception: the parent Y. pestis KIM5 but not the YopM(-) mutant caused a significant global decrease in NK cell numbers (blood, spleen, and liver), beginning early in infection. NK cells and macrophages isolated early (day 2) from livers and spleens of mice infected with either Y. pestis strain contained comparable levels of cytokine mRNA: interleukin (IL)-1 beta, IL-12, IL-15, IL-18, and tumor necrosis factor alpha in macrophages and gamma interferon in NK cells. However, by day 4 postinfection, cells from mice infected with the parent Y. pestis expressed lower levels of these messages, while those from mice infected with the mutant retained strong expression. Significantly, mRNA for the IL-15 receptor alpha chain was not expressed in NK cells from Y. pestis KIM5-infected mice as early as day 2 postinfection. These findings suggest that YopM interferes with innate immunity by causing depletion of NK cells, possibly by affecting the expression of IL-15 receptor alpha and IL-15.

Type iii protein secretion in yersinia species

The type III mechanism of protein secretion is a pathogenic strategy shared by a number of gram-negative pathogens of plants and animals that has evolved in order to inject virulence proteins into the cytosol of target eukaryotic cells. The pathogens of the Yersinia genus represent a model system where much progress has been made in understanding this secretion pathway. Herein, we review what has been recently learned in yersiniae about the various environmental signals that induce type III secretion, how the synthesis of secretion substrates is regulated, and how such a diverse group of proteins is recognized as a substrate for secretion.

Differential modulation by Ca2+ of type III secretion of diffusely adhering enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) strains are a common cause of persistent diarrhea among infants, primarily in developing countries. The pathogenicity of EPEC is associated with the expression and secretion of bacterial proteins encoded by the chromosomal locus of enterocyte effacement (LEE). The LEE-encoded type III-secreted proteins EspA, EspB, and EspD are part of a molecular syringe, which is used by EPEC to translocate effector proteins directly into the cytoplasm of host cells. The type III-secreted translocated intimin receptor (Tir) protein is thought to be delivered by an Esp-dependent mechanism into the host cell, and this is followed by insertion into the host plasma membrane, where the protein serves as the receptor for intimin, an afimbrial bacterial adhesin. Type III secretion is subject to environmental regulation, and secretion can be induced in vitro by growing bacteria in cell culture medium. In this study we found that Ca(2+) is involved in the regulation of type III secretion both in classical locally adherent EPEC and in atypical diffusely adherent EPEC. Interestingly, we observed contrasting secretion of Esp proteins and Tir in response to Ca(2+). While the secretion of Tir is clearly enhanced and the protein is integrated into HeLa membranes under calcium chelation conditions, Esp secretion is strongly reduced under these conditions. These data suggest that under Ca(2+)-depleted conditions Tir might be secreted into the medium and integrated into host membranes by an Esp-independent mechanism, without the need for a functional type III translocation machinery.

Differential stimulation of helper and cytotoxic T cells by dendritic cells after infection by Yersinia enterocolitica in vitro

Dendritic cells (DC) are antigen-presenting cells crucial for initiating immune responses like sensitization of T cells to foreign antigens. We have previously shown that infection of DC by enteropathogenic Yersinia enterocolitica in vitro leads to a transient suppression in the immunostimulatory capacity for autologous enriched total T cells. In this study, we found that killed Yersinia could replace live bacteria in this aspect, and that yersinial lipopolysaccharide (LPS)-antigen could be detected intracellularly over a time course of 8 days. A suppressive effect on T cell proliferation after stimulation with Yersinia-infected compared to uninfected DC was seen for CD4+ T cells isolated by immunomagnetic separation techniques over the whole time course of 8 days, whereas CD8+ T cells followed to exhibit a suppressed proliferation rate starting on day 5 post infection till the end of the time course. In contrast, enriched total T cells stimulated by Yersinia-infected DC showed weaker proliferation till day 6 post infection compared to stimulation by uninfected DC, but not thereafter. Mixing of purified CD4+ and CD8+ T cells at day 8 post infection could reconstitute the effect seen for enriched total T cells. Thus, helper in concert with cytotoxic T cells might contribute to the immune responses, that are necessary for control of Yersinia-infections.

CAS/Crk signalling mediates uptake of Yersinia into human epithelial cells

Uptake of Yersinia pseudotuberculosis into mammalian cells involves engagement of beta1 integrin receptors by the bacterial protein invasin. This triggers a host response that involves tyrosine phosphorylation of proteins and the induction of actin rearrangements that lead to cellular uptake of bacteria. In this report, we show that the focal adhesion protein CAS plays an important role in Yersinia uptake, and that its function is linked to the phosphorylation-dependent interaction between CAS and Crk. These studies demonstrate that Yersinia binding to host cell receptors initiates a cascade of events involving tyrosine phosphorylation of CAS, subsequent formation of functional CAS-Crk complexes and the activity of the small GTP-binding protein Rac1. The delineation of this pathway lends support for a model in which Yersinia uptake into human epithelial cells is dependent upon aspects of host signalling pathways that govern actin cytoskeleton remodelling and cell migration.

Virulence plasmid (pYV)-associated susceptibility of Yersinia enterocolitica to chlorine and heavy metals

This study was aimed at elucidating the role of virulence plasmid (pYV) in the susceptibility of Yersinia enterocolitica to bactericidal agents such as chlorine and heavy metals. Plasmid-bearing (pYV+) Y. enterocolitica was less susceptible to the antimicrobial action of chlorine and heavy metals compared with the isogenic plasmidless (pYV-) derivative. This difference was, however, observed only with bacteria cultured at 25 degrees C. pYV-associated susceptibility apart, cells cultured at 37 degrees C were also found to be less susceptible to the antimicrobial action of these agents. The results indicate that the susceptibility of Y. enterocolitica to these agents was influenced both by the presence of the virulence plasmid and the temperature at which the cells were cultured.

The Yersinia tyrosine phosphatase YopH targets a novel adhesion-regulated signalling complex in macrophages

The Yersinia protein tyrosine phosphatase (PTP) YopH is translocated into eukaryotic cells by a type III secretion system that requires bacterial-host cell contact. YopH is composed of two modular effector domains: a substrate-binding domain located in the N-terminal region (residues 1-130) and a PTP catalytic domain located in the C-terminal region (residues 206-468). Previous studies have shown that YopH selectively targets tyrosine-phosphorylated proteins of approximate molecular weight 120 kDa (p120) and 55 kDa (p55) in murine macrophages. It has been demonstrated that p120 actually represents two tyrosine-phosphorylated target proteins, Cas and Fyb. We used the substrate-binding domain of YopH to affinity purify tyrosine-phosphorylated target proteins from lysates of J774A.1 macrophages. Protein microsequencing identified p55 as murine SKAP-HOM. Direct interaction between SKAP-HOM and a catalytically inactive form of YopH was demonstrated in vitro and in macrophages. In addition, we obtained evidence that SKAP-HOM is tyrosine phosphorylated in response to macrophage cell adhesion and that it forms a signalling complex with Fyb. We suggest that dephosphorylation of SKAP-HOM and Fyb by YopH allows yersiniae to interfere with a novel adhesion-regulated signal transduction pathway in macrophages.

The RhoGAP activity of the Yersinia pseudotuberculosis cytotoxin YopE is required for antiphagocytic function and virulence

A variety of pathogenic bacteria use type III secretion pathways to translocate virulence proteins into host eukaryotic cells. YopE is an important virulence factor that is translocated into mammalian cells via a plasmid-encoded type III system in Yersinia spp. YopE action in mammalian cells promotes the disruption of actin filaments, cell rounding and blockage of phagocytosis. It was reported recently that two proteins with sequence similarity to YopE, SptP of Salmonella typhimurium and ExoS of Pseudomonas aeruginosa, function as GTPase-activating proteins (GAPs) for Rho GTPases. YopE contains an 'arginine finger' motif that is present in SptP, ExoS and other Rho GAPs and is essential for catalysis by this class of proteins. We show here that a GST-YopE fusion protein stimulated in vitro GTP hydrolysis by the Rho family members Cdc42, RhoA and Rac1, but not by Ras. Conversion of the essential arginine in the arginine finger motif to alanine (R144A) eliminated the in vitro GAP activity of GST-YopE. Infection assays carried out with a Yersinia pseudotuberculosis strain producing YopER144A demonstrated that GAP function was essential for the disruption of actin filaments, cell rounding and inhibition of phagocytosis by YopE in HeLa cells. Furthermore, the GAP function of YopE was important for Y. pseudotuberculosis pathogenesis in a mouse infection assay. Transfection of HeLa cells with a vector that produces a constitutively active form of RhoA (RhoA-V14) prevented the disruption of actin filaments and cell rounding by YopE. Production of an activated form of Rac1 (Rac1-V12), but not RhoA-V14, in HeLa cells interfered with YopE antiphagocytic activity. These results demonstrate that YopE functions as a RhoGAP to downregulate multiple Rho GTPases, leading to the disruption of actin filaments and inhibition of bacterial uptake into host cells.

The response regulator PhoP is important for survival under conditions of macrophage-induced stress and virulence in Yersinia pestis

The two-component regulatory system PhoPQ has been identified in many bacterial species. However, the role of PhoPQ in regulating virulence gene expression in pathogenic bacteria has been characterized only in Salmonella species. We have identified, cloned, and sequenced PhoP orthologues from Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica. To investigate the role of PhoP in the pathogenicity of Y. pestis, an isogenic phoP mutant was constructed by using a reverse-genetics PCR-based strategy. The protein profiles of the wild-type and phoP mutant strains, grown at either 28 or 37 degrees C, revealed more than 20 differences, indicating that PhoP has pleiotrophic effects on gene expression in Y. pestis. The mutant showed a reduced ability to survive in J774 macrophage cell cultures and under conditions of low pH and oxidative stress in vitro. The mean lethal dose of the phoP mutant in mice was increased 75-fold in comparison with that of the wild-type strain, indicating that the PhoPQ system plays a key role in regulating the virulence of Y. pestis.

Investigation into the role of the serine protease HtrA in Yersinia pestis pathogenesis

The HtrA stress response protein has been shown to play a role in the virulence of a number of pathogens. For some organisms, htrA mutants are attenuated in the animal model and can be used as live vaccines. A Yersinia pestis htrA orthologue was identified, cloned and sequenced, showing 86% and 87% similarity to Escherichia coli and Salmonella typhimurium HtrAs. An isogenic Y. pestis htrA mutant was constructed using a reverse genetics approach. In contrast to the wild-type strain, the mutant failed to grow at an elevated temperature of 39 degrees C, but showed only a small increase in sensitivity to oxidative stress and was only partially attenuated in the animal model. However, the mutant exhibited a different protein expression profile to that of the wild-type strain when grown at 28 degrees C to simulate growth in the flea.

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.

Reciprocal secretion of proteins by the bacterial type III machines of plant and animal pathogens suggests universal recognition of mRNA targeting signals

Bacterial pathogens of both animals and plants use type III secretion machines to inject virulence proteins into host cells. Although many components of the secretion machinery are conserved among different bacterial species, the substrates for their type III pathways are not. The Yersinia type III machinery recognizes some secretion substrates via a signal that is encoded within the first 15 codons of yop mRNA. These signals can be altered by frameshift mutations without affecting secretion of the encoded polypeptides, suggesting a mechanism whereby translation of yop mRNA is coupled to the translocation of newly synthesized polypeptide. We report that the type III machinery of Erwinia chrysanthemi cloned in Escherichia coli recognizes the secretion signals of yopE and yopQ. Pseudomonas syringae AvrB and AvrPto, two proteins exported by the recombinant Erwinia machine, can also be secreted by the Yersinia type III pathway. Mapping AvrPto sequences sufficient for the secretion of reporter fusions in Yersinia revealed the presence of an mRNA secretion signal. We propose that 11 conserved components of type III secretion machines may recognize signals that couple mRNA translation to polypeptide secretion.

Inhibition of the mitogen-activated protein kinase kinase superfamily by a Yersinia effector

The bacterial pathogen Yersinia uses a type III secretion system to inject several virulence factors into target cells. One of the Yersinia virulence factors, YopJ, was shown to bind directly to the superfamily of MAPK (mitogen-activated protein kinase) kinases (MKKs) blocking both phosphorylation and subsequent activation of the MKKs. These results explain the diverse activities of YopJ in inhibiting the extracellular signal-regulated kinase, c-Jun amino-terminal kinase, p38, and nuclear factor kappa B signaling pathways, preventing cytokine synthesis and promoting apoptosis. YopJ-related proteins that are found in a number of bacterial pathogens of animals and plants may function to block MKKs so that host signaling responses can be modulated upon infection.

Cytotoxic T-cell-mediated response against Yersinia pseudotuberculosis in HLA-B27 transgenic rat

Yersinia-induced reactive arthritis is highly associated with HLA-B27, the role of which in defense against the triggering bacteria remains unclear. The aim of this study was to examine the capacity of rats transgenic for HLA-B27 to mount a cytotoxic T-lymphocyte (CTL) response against Y. pseudotuberculosis and to determine the influence of the HLA-B27 transgene on this response. Rats transgenic for HLA-B*2705 and human beta(2)-microglobulin of the 21-4L line, which do not spontaneously develop disease, and nontransgenic syngeneic Lewis (LEW) rats were infected with Y. pseudotuberculosis. Lymph node cells were restimulated in vitro, and the presence of for Y. pseudotuberculosis-specific CTLs against infected targets was determined. Infection of 21-4L rats triggered a CD8(+) T cell-mediated cytotoxic response specific for Y. pseudotuberculosis. Analysis of this response demonstrated restriction by an endogenous major histocompatibility complex molecule. However, no restriction by HLA-B27 was detected. In addition, kinetics studies revealed a weaker anti-Yersinia CTL response in 21-4L rats than in nontransgenic LEW rats, and the level of cytotoxicity against 21-4L lymphoblast targets sensitized with Y. pseudotuberculosis was lower than that against nontransgenic LEW targets. We conclude that HLA-B27 transgenic rats mount a CTL response against Y. pseudotuberculosis that is not restricted by HLA-B27. Yet, HLA-B27 exerts a negative effect on the level of this response, which could contribute to impaired defense against Yersinia.

Immune response to Yersinia outer proteins and other Yersinia pestis antigens after experimental plague infection in mice

There is limited information concerning the nature and extent of the immune response to the virulence determinants of Yersinia pestis during the course of plague infection. In this study, we evaluated the humoral immune response of mice that survived lethal Y. pestis aerosol challenge after antibiotic treatment. Such a model may replicate the clinical situation in humans and indicate which virulence determinants are expressed in vivo. Immunoglobulin G enzyme-linked immunosorbent assay and immunoblotting were performed by using purified, recombinant antigens including F1, V antigen, YpkA, YopH, YopM, YopB, YopD, YopN, YopE, YopK, plasminogen activator protease (Pla), and pH 6 antigen as well as purified lipopolysaccharide. The major antigens recognized by murine convalescent sera were F1, V antigen, YopH, YopM, YopD, and Pla. Early treatment with antibiotics tended to reduce the immune response and differences between antibiotic treatment regimens were noted. These results may indicate that only some virulence factors are expressed and/or immunogenic during infection. This information may prove useful for selecting potential vaccine candidates and for developing improved serologic diagnostic assays.

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.

Type III machines of pathogenic yersiniae secrete virulence factors into the extracellular milieu

Gram-negative bacteria use type III machines to inject toxic proteins into the cytosol of eukaryotic cells. Pathogenic Yersinia species export 14 Yop proteins by the type III pathway and some of these, named effector Yops, are targeted into macrophages, thereby preventing phagocytosis and allowing bacterial replication within lymphoid tissues. Hitherto, YopB/YopD were thought to insert into the plasma membrane of macrophages and to promote the import of effector Yops into the eukaryotic cytosol. We show here that the type III machines of yersiniae secrete three proteins into the extracellular milieu (YopB, YopD and YopR). Although intrabacterial YopD is required for the injection of toxins into eukaryotic cells, secreted YopB, YopD and YopR are dispensable for this process. Nevertheless, YopB, YopD and YopR are essential for the establishment of Yersinia infections in a mouse model system, suggesting that type III secretion machines function to deliver virulence factors into the extracellular milieu also.

Coordinate Involvement of Invasin and Yop Proteins in a Yersinia pseudotuberculosis-Specific Class I-Restricted Cytotoxic T Cell-Mediated Response

Yersinia pseudotuberculosis is a pathogenic enteric bacteria that evades host cellular immune response and resides extracellularly in vivo. Nevertheless, an important contribution of T cells to defense against Yersinia has been previously established. In this study we demonstrate that Lewis rats infected with virulent strains of Y. pseudotuberculosis, mount a Yersinia-specific, RT1-A-restricted, CD8+ T cell-mediated, cytotoxic response. Sensitization of lymphoblast target cells for cytolysis by Yersinia-specific CTLs required their incubation with live Yersinia and was independent of endocytosis. Although fully virulent Yersinia did not invade those cells, they attached to their surface. In contrast, invasin-deficient strain failed to bind to blast targets or to sensitize them for cytolysis. Furthermore, an intact virulence plasmid was an absolute requirement for Yersinia to sensitize blast targets for cytolysis. Using a series of Y. pseudotuberculosis mutants selectively deficient in virulence plasmid-encoded proteins, we found no evidence for a specific role played by YadA, YopH, YpkA, or YopJ in the sensitization process of blast targets. In contrast, mutations suppressing YopB, YopD, or YopE expression abolished the capacity of Yersinia to sensitize blast targets. These results are consistent with a model in which extracellular Yersinia bound to lymphoblast targets via invasin translocate inside eukaryotic cytosol YopE, which is presented in a class I-restricted fashion to CD8+ cytotoxic T cells. This system could represent a more general mechanism by which bacteria harboring a host cell contact-dependent or type III secretion apparatus trigger a class I-restricted CD8+ T cell response.

Yersinia enterocolitica type III secretion: an mRNA signal that couples translation and secretion of YopQ

Pathogenic Yersinia species export Yop proteins via a type III machinery to escape their phagocytic killing during animal infections. Here, we reveal the type III export mechanism of YopQ. In the presence of calcium, when type III secretion was blocked, yopQ mRNA was not translated. The signal of YopQ sufficient for the secretion of translationally fused reporter proteins was contained within the first 10 codons of its open reading frame. Some frameshift mutations that completely altered the peptide sequence specified by this signal did not impair secretion of the reporter protein. Exchanging the upstream untranslated mRNA leader of yopQ for that of E. coli lacZ also did not affect secretion. However, removal of the first 15 codons abolished YopQ export. Pulse-labelled YopE, but not YopQ, could be secreted after the polypeptide had been synthesized within the cytoplasm of Yersinia (post-translational secretion). Thus, YopQ appears to be exported by a mechanism that couples yopQ mRNA translation with the type III secretion of the encoded polypeptide.

Type III machines of Gram-negative pathogens: injecting virulence factors into host cells and more

Many Gram-negative bacteria that cause disease in either mammals or plants share a strategy of delivering toxic proteins into the cytoplasm of host cells known as type III secretion. Recent advances have provided a glimpse at the molecular nature of these lethal injection machines. Several groups have reported fibrous structures on bacterial surfaces that appear to be extensions of type III machines and necessary for toxin injection into host cells. Other research revealed complex mechanisms of secretion substrate recognition that presumably function to direct toxins to different locations during infection.

YopJ of Yersinia spp. is sufficient to cause downregulation of multiple mitogen-activated protein kinases in eukaryotic cells

Pathogenic Yersinia spp. utilize a plasmid-encoded type III secretion system to deliver a set of Yop effector proteins into eukaryotic cells. Previous studies have shown that the effector YopJ is required for Yersinia to cause downregulation of the mitogen-activated protein (MAP) kinases c-Jun N-terminal kinase (JNK), p38, and extracellular signal-regulated kinase (ERK) 1 and 2 in infected macrophages. Here we demonstrate that YopJ is sufficient to cause downregulation of multiple MAP kinases in eukaryotic cells. Cellular fractionation experiments confirmed that YopJ is delivered into the cytoplasmic fraction of macrophages by the type III system. Production of YopJ in COS-1 cells by transfection significantly reduced (5- to 10-fold) activation of JNK, p38, and ERK in response to several different stimuli, including serum and tumor necrosis factor alpha. JNK activation mediated by RacV12, an activated mutant of Rac1, was also blocked by YopJ in COS-1 cells, indicating that YopJ acts downstream of this small GTPase to downregulate MAP kinase signaling. Analysis of transfected COS-1 cells by immunofluorescence microscopy revealed that YopJ is recruited from the cytoplasmic compartment to the cell periphery in response to stimuli (e.g., serum) that induce membrane ruffling. These data indicate that YopJ functions as a "MAP kinase toxin" to selectively block nuclear responses that are triggered by Yersinia-host cell interaction.

Identification and characterization of SpcU, a chaperone required for efficient secretion of the ExoU cytotoxin

In recent studies, we have shown that Pseudomonas aeruginosa strains that are acutely cytotoxic in vitro damage the lung epithelium in vivo. Genetic analysis indicated that the factor responsible for acute cytotoxicity was controlled by ExsA and therefore was part of the exoenzyme S regulon. The specific virulence determinant responsible for epithelial damage in vivo and cytotoxicity in vitro was subsequently mapped to the exoU locus. The present studies are focused on a genetic characterization of the exoU locus. Northern blot analyses and complementation experiments indicated that a region downstream of exoU was expressed and that the expression of this region corresponded to increased ExoU secretion. DNA sequence analysis of a region downstream of exoU identified several potential coding regions. One of these open reading frames, SpcU (specific Pseudomonas chaperone for ExoU), encoded a small 15-kDa acidic protein (137 amino acids [pI 4.4]) that possessed a leucine-rich motif associated with the Syc family of cytosolic chaperones for the Yersinia Yops. T7 expression analysis and nickel chromatography of histidine-tagged proteins indicated that ExoU and SpcU associated as a noncovalent complex when coexpressed in Escherichia coli. The association of ExoU and SpcU required amino acids 3 to 123 of ExoU. In P. aeruginosa, ExoU and SpcU are coordinately expressed as an operon that is controlled at the transcriptional level by ExsA.

Targeting of the Yersinia pestis YopM protein into HeLa cells and intracellular trafficking to the nucleus

The YopM virulence protein of Yersinia pestis has been described as binding human alpha-thrombin and inhibiting thrombin-induced platelet aggregation in vitro. However, recent studies have shown that a YopM-CyaA fusion protein could be targeted vectorially into eukaryotic cells through the Yersinia type III secretion system. In this study, our objective was to characterize YopM's fate in more detail. We followed YopM in the culture medium and inside infected HeLa cells. We confirmed that the native YopM is targeted into HeLa cells, where it is insensitive to exogenous trypsin. The bacteria must be surface located to target YopM, and YopB and YopD are necessary, whereas the LcrE protein (called also YopN) makes this process more efficient. Immunofluorescence localization revealed that YopM, in contrast to YopE, is not only targeted to the cytoplasm but also trafficks to the cell's nucleus by means of a vesicle-associated pathway that is strongly inhibited by brefeldin A, perturbed by monensin or bafilomycin A1 and dependent upon microtubules (decreased by colchicine and nocodazole). These findings revealed a novel interaction of Yersinia pestis with its eukaryotic host.

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.

A complex composed of SycN and YscB functions as a specific chaperone for YopN in Yersinia pestis

Human pathogenic Yersinia resist host defences, in part through the expression and delivery of a set of plasmid-encoded virulence proteins termed Yops. A number of these Yops are exported from the bacteria directly into the cytoplasm of their eukaryotic host's cells upon contact with these cells. The secreted YopN protein (also known as LcrE) is required to block Yop secretion in the presence of calcium in vitro or before contact with a eukaryotic cell in vivo. In this study, we characterize the role of the tyeA, sycN and yscB gene products in the regulation of Yop secretion in Yersinia pestis. Mutants specifically defective in the expression of TyeA, SycN or YscB were no longer able to block Yop secretion in the presence of calcium. In addition, the secretion of YopN was specifically reduced in both the sycN and the yscB deletion mutants. Protein cross-linking and immunoprecipitation studies in conjunction with yeast two-hybrid analyses showed that SycN and YscB interact with one another to form a SycN/YscB complex. Yeast three-hybrid analyses demonstrated that the SycN/YscB complex, but not SycN or YscB alone, specifically associates with YopN. SycN and YscB share amino acid sequence similarity and structural similarities with the specific Yop chaperones SycE and SycH. Together, these results indicate that a complex composed of SycN and YscB functions as a specific chaperone for YopN in Y. pestis.

In vitro and in vivo expression studies of yopE from Yersinia enterocolitica using the gfp reporter gene

The Yersinia outer protein YopE belongs to the translocated effector proteins of pathogenic yersiniae. We constructed various truncated yopE genes fused to gfp (encoding the green fluorescent protein) to study yopE gene expression and YopE-GFP translocation of Y. enterocolitica in cell culture and mouse infection models. The hybrid gene fusions were co-expressed in Y. enterocolitica (i) on a low-copy plasmid in the presence of the virulence plasmid pYV08 (in trans configuration) and (ii) after co-integration by homologous recombination of a yopE-gfp-carrying suicide plasmid into pYV08 (co-integrate configuration). After 30min of infection of HEp-2 cell monolayers, extracellularly located yersiniae began to emit green fluorescence after excitation. In contrast, internalized bacteria were weakly fluorescent. Translocation of YopE-GFP into HEp-2 cells by attached yersiniae was visualized by optical sectioning of fluorescent HEp-2 cells using confocal laser scanning microscopy and was confirmed by immunoprecipitation of cytosolic YopE-GFP from selectively solubilized HEp-2 cells. The co-translocation of other Yops was not significantly impaired by YopE-GFP as shown by YopH/YopE-mediated suppression of the oxidative burst of infected neutrophils. The time course of yopE-gfp expression (in trans as well as in the co-integrate configuration) in the HEp-2 cell infection model as well as after in vitro induction was studied using a highly sensitive CCD camera and a flow cytometer. Similar results were obtained with a YopE-LUC (firefly luciferase) protein fusion as reporter. After intraperitoneal, intravenous and orogastrical infection of Balb/c mice with the recombinant yersiniae strains, green fluorescing bacteria could be visualized microscopically in the peritoneum, the spleen, the liver and in the Peyer's patches. However, only weakly fluorescent yersiniae were observed in the intestinal lumen. These results were quantified by flow cytometric measurements. The application of gfp as a reporter gene turned out to be promising for the study of protein translocation by protein type III secretion systems and differential virulence gene expression in vivo.