Search

Vibrio parahaemolyticus harbors two type III secretion systems (T3SSs; T3SS1 and T3SS2), of which T3SS1 is involved in host cell cytotoxicity. T3SSI expression is positively regulated by ExsA, and it is negatively regulated by ExsD. We compared the secretion profiles of a wild-type strain (NY-4) of V. parahaemolyticus with those of an ExsD deletion mutant ([DELTA]exsD) and with a strain of NY-4 that overexpresses T3SSI (NY-4:pexsA). From this comparison, we detected a previously uncharacterized protein, Vp1659, which shares some sequence homology with LcrV from Yersinia. We show that vp1659 expression is positively regulated by ExsA and is negatively regulated by ExsD. Vp1659 is specifically secreted by T3SS1 of V. parahaemolyticus, and Vp1659 is not required for the successful extracellular secretion of another T3SSI protein, Vp1656. Mechanical fractionation showed that Vp1659 is translocated into HeLa cells in a T3SSl-dependent manner and that deletion of Vp1659 does not prevent VopS from being translocated into HeLa cells during infection. Deletion of vp1659 significantly reduces cytotoxicity when HeLa cells are infected by V. parahaemolyticus, while complementation of the [DELTA]vp1659 strain restores cytotoxicity. Differential staining showed that Vp1659 is required to induce membrane permeability in HeLa cells. We also show evidence that Vp1659 is required for actin rearrangement and the induction of autophagy. On the basis of these data, we conclude that Vp1659 is a T3SSl-associated protein that is a component of the secretion apparatus and that it is necessary for the efficient translocation of effector proteins into epithelial cells. doi: 10.1128/JB.01493-09

Campylobacter jejuni is one of the most frequent bacterial causes of food-borne gastrointestinal disease in developed countries. Previous work indicates that the binding of C. jejuni to human intestinal cells is crucial for host colonization and disease. Fibronectin (Fn), a major constituent of the extracellular matrix, is a ~250-kDa glycoprotein present at regions of cell-to-cell contact in the intestinal epithelium. Fn is composed of three types of repeating units: type I (~45 amino acids), type II (~60 amino acids), and type III (~90 amino acids). The deduced amino acid sequence of C. jejuni flpA (Cj1279c) contains at least three Fn type HI domains. Based on the presence of the Fn type HI domains, we hypothesized that FlpA contributes to the binding of C. jejuni to human INT 407 epithelial cells and Fn. We assessed the contribution of FlpA in C. jejuni binding to host cells by in vitro adherence assays with a C. jejuni wild-type strain and a C. jejuni flpA mutant and binding of purified FlpA protein to Fn by enzyme-linked immunosorbent assay (ELISA). Adherence assays revealed the binding of the C. jejuni flpA mutant to INT 407 epithelial cells was significantly reduced compared with that for a wild-type strain. In addition, rabbit polyclonal serum generated against FlpA blocked C. jejuni adherence to INT 407 cells in a concentration-dependent manner. Binding of FlpA to Fn was found to be dose dependent and saturable by ELISA, demonstrating the specificity of the interaction. Based on these data, we conclude that FlpA mediates C. jejuni attachment to host epithelial cells via Fn binding. doi: 10.1128/JB.00969-09

The Vibrio parahaemolyticus type III secretion system 1 (T3SS1) induces cytotoxicity in mammalian epithelial cells. We characterized the cell death phenotype in both epithelial (HeLa) and monocytic (U937) cell lines following infection with V. parahaemolyticus. Using a combination of the wild-type strain and gene knockouts, we confirmed that V. parahaemolyticus strain NY-4 was able to induce cell death in both cell lines via a T3SSl-dependent mechanism. Bacterial contact, but not internalization, was required for T3SSl-induced cytotoxicity. The mechanism of cell death involves formation of a pore structure on the surface of infected HeLa and U937 cells, as demonstrated by cellular swelling, uptake of cell membrane-impermeable dye and protection of cytotoxicity by osmoprotectant (PEG3350). Western blot analysis showed that poly ADP ribose polymerase (PARP) was not cleaved and remained in its full-length active form. This result was evident for seven different V. parahaemolyticus strains. V. parahaemolyticus-induced cytotoxicity was not inhibited by addition of the pan-caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (Z-VAD-FMK) or the caspase-1 inhibitor N-acetyl-tyrosyl-valylalanyl-aspartyl-aldehyde (Ac-YVAD-CHO); thus, caspases were not involved in T3SSl-induced cytotoxicity. DNA fragmentation was not evident following infection and autophagic vacuoles were not observed after monodansylcadaverine staining. We conclude that T3SS1 of V. parahaemolyticus strain NY-4 induces a host cell death primarily via oncosis rather than apoptosis, pyroptosis or autophagy.

Campylobacter jejuni is a major food-borne bacterial pathogen, which is capable of causing diarrhoea containing blood and leukocytes. C. jejuni invasion of the intestinal epithelial cells and the release of proinflammatory molecules contribute to the pathophysiology of campylobacteriosis. Given the commensal relationship of C. jejuni with chickens, we hypothesized that C. jejuni invasion of chicken cells and the release of host cell cytokines would be significantly less than with human cells. To test our hypothesis, we examined the interactions of C. jejuni with chicken LMH cells, and performed in vivo experiments with chickens. The binding and internalization assays revealed that C. jejuni was significantly less invasive of LMH cells relative to human INT 407 cells, even though the bacteria bound to each host cell species equally. We also assessed interleukin-8 (IL-8) transcript, IL-8 secretion, and the release of chemoattractant molecules from the inoculated cells. Inoculation of LMH cells with C. jejuni stimulated expression of both chicken IL-8 orthologues, chCXCLi2 and chCXCLi1, but at levels significantly less than human IL-8 (huCXCL8) expressed from human INT 407 cells inoculated with C. jejuni. Moreover, the supernatant fluids of the C. jejuni-inoculated LMH cells resulted in little heterophil migration. In vivo, C. jejuni were observed bound to the cells lining the glandular crypts, but overt signs of cell invasion or pathology were not observed. These results indicate that cytokine expression in chicken LMH cells in response to C. jejuni is distinct from that of Salmonella typhimurium.

Campylobacter jejuni, a spiral-shaped gram-negative bacterium, is a leading bacterial cause of human food-borne illness. Acute disease is associated with C. jejuni invasion of the intestinal epithelium. Further, maximal host cell invasion requires the secretion of proteins termed Campylobacter invasion antigens (Cia). As bile acids are known to alter the pathogenic behavior of other gastrointestinal pathogens, we hypothesized that the virulence potential of Campylobacter may be triggered by the bile acid deoxycholate (DOC). In support of this hypothesis, culturing C. jejuni with a physiologically relevant concentration of DOC significantly altered the kinetics of cell invasion, as shown by gentamicin protection assays. In contrast to C. jejuni harvested from Mueller-Hinton (MH) agar plates, C. jejuni harvested from MH agar plates supplemented with DOC secreted the Cia proteins, as judged by metabolic labeling experiments. DOC was also found to induce the expression of the ciaB gene, as determined by [beta]-galactosidase reporter, real-time reverse transcription-PCR, and microarray analyses. Microarray analysis further revealed that DOC induced the expression of virulence genes (ciaB, cmeABC, dccR, and tlyA). In summary, we demonstrated that it is possible to enhance the pathogenic behavior of C. jejuni by modifying the culture conditions. These results provide a foundation for identifying genes expressed by C. jejuni in response to in vivo-like culture conditions.

In vitro and in vivo adherence and colonization assays are performed with Campylobacter jejuni clinical strain (F38011) and Campylobacter jejuni strain recovered from a chicken (02-833L) in order to understand the bacterium-host cell interactions. Campylobacter jejuni strains have competed for colonization in chicks and a novel intervention strategy is designed for reducing the level at which these strains colonizes the cecum.

Two-component regulatory systems play a major role in the physiological response of bacteria to environmental stimuli. Such systems are composed of a sensor histidine kinase and a response regulator whose ultimate function is to affect the expression of target genes. Response regulator mutants of Campylobacter jejuni strain F38011 were screened for sensitivity to sodium deoxycholate. A mutation in Cj0643, which encodes a response regulator with no obvious cognate histidine kinase, resulted in an absence of growth on plates containing a subinhibitory concentration of sodium deoxcholate (1%, wt/vol). In broth cultures containing 0.05% (wt/vol) sodium deoxycholate, growth of the mutant was significantly inhibited compared to growth of the C. jejuni F38011 wild-type strain. Complementation of the C.jejuni cbrR mutant in trans restored growth in both broth and plate cultures supplemented with sodium deoxycholate. Based on the phenotype displayed by its mutation, we designated the gene corresponding to Cj0643 as cbrR (Campylobacter bile resistance regulator). While the MICs of a variety of bile salts and other detergents for the C. jejuni cbrR mutant were lower, no difference was noted in its sensitivity to antibiotics or osmolarity. Finally, chicken colonization studies demonstrated that the C. jejuni cbrR mutant had a reduced ability to colonize compared to the wild-type strain. These data support previous findings that bile resistance contributes to colonization of chickens and establish that the response regulator, CbrR, modulates resistance to bile salts in C. jejuni.

Campylobacter jejuni, a gram-negative motile bacterium, secretes a set of proteins termed the Campylobacter invasion antigens (Cia proteins). The purpose of this study was to determine whether the flagellar apparatus serves as the export apparatus for the Cia proteins. Mutations were generated in five genes encoding three structural components of the flagella, the flagellar basal body (flgB and flgC), hook (flgE2), and filament (flaA and flaB) genes, as well as in genes whose products are essential for flagellar protein export (flhB and fliI). While mutations that affected filament assembly were found to be nonmotile ([Mot.sup.-]) and did not secrete Cia proteins ([S.sup.-]), a flaA (fla[B.sup.+]) filament mutant was found to be nonmotile but Cia protein secretion competent ([Mot.sup.-], [S.sup.+]). Complementation of a flaA flaB double mutant with a shuttle plasmid harboring either the flaA or flaB gene restored Cia protein secretion, suggesting that Cia export requires at least one of the two filament proteins. Infection of INT 407 human intestinal cells with the C.jejuni mutants revealed that maximal invasion of the epithelial cells required motile bacteria that are secretion competent. Collectively, these data suggest that the C. jejuni Cia proteins are secreted from the flagellar export apparatus.

Apoptosis induction of host macrophages has emerged as a common virulence mechanism among bacterial pathogens. Infection with Campylobacter jejuni is a leading cause of gastroenteritis worldwide and is characterized by an acute inflammatory response in the small intestine. The authors used the human monocytic cell line THP-1 to examine apoptosis induction and pro-inflammatory cytokine production during C. jejuni infection. Flow cytometric analysis revealed that 48 h after inoculation, a C. jejuni wild-type isolate induced apoptosis in 630/0 of THP-1 cells while only 34% of cells inoculated with a ciaB mutant, which does not secrete the Cia (Campylobacter invasion antigens) proteins, underwent apoptosis. Complementation of the ciaB mutant resulted in levels of apoptosis similar to those induced by the C. jejuni wild-type isolate, suggesting that the Cia proteins have a role in apoptosis induction. It was shown that a proteinase K- and heat-stable component of C. jejuni also stimulated THP-1 apoptosis. Inoculation with a C. jejuni gmhD mutant indicated that lipooligosaccharide was not the stimulatory molecule. Immunoblot and ELISA analyses revealed that C. jejuni infection stimulated the synthesis, processing and secretion of interleukin 1[beta] (IL-1[beta]). Inhibition of caspase 1 activity eliminated IL-1[beta] processing and secretion, but did not affect apoptosis induction. In addition, treatment of cells with a caspase-9-specific inhibitor did not affect apoptosis induction, arguing against activation of an apoptotic pathway dependent on either caspase 1 or 9 activation. Collectively, these data suggest that the inoculation of macrophages with C. jejuni results in the processing of IL-1[beta] and apoptosis through different regulatory pathways. Furthermore, these data argue that C. jejuni may use a mechanism distinct from Salmonella typhimurium and Shigella flexneri to initiate macrophage apoptosis and release of IL-1[beta].

Research has been conducted on Campylobacter jejuni. The binding of this bacterium to fibronectin via outer-membrane proteins CadF has been investigated, and the results suggest that CadF promotes the binding of C. jejuni to fibronectin.

Horizontal gene transfer (HGT) is a driving force for the dissemination of antimicrobial resistance (AMR) genes among Campylobacter jejuni organisms, a leading cause of foodborne gastroenteritis worldwide. Although HGT is well documented for C. jejuni planktonic cells, the role of C. jejuni biofilms in AMR spread that likely occurs in the environment is poorly understood. Here, we developed a cocultivation model to investigate the HGT of chromosomally encoded AMR genes between two C. jejuni F38011 AMR mutants in biofilms. Compared to planktonic cells, C. jejuni biofilms significantly promoted HGT (P,0.05), resulting in an increase of HGT frequencies by up to 17.5-fold. Dynamic study revealed that HGT in biofilms increased at the early stage (i.e., from 24 h to 48 h) and remained stable during 48 to 72 h. Biofilms continuously released the HGT mutants into supernatant culture, indicating spontaneous dissemination of AMR to broader niches. DNase I treatment confirmed the role of natural transformation in genetic exchange. HGT was not associated with biofilm biomass, cell density, or bacterial metabolic activity, whereas the presence of extracellular DNA was negatively correlated with the altered HGT frequencies. HGT in biofilms also had a strain-to-strain variation. A synergistic HGT effect was observed between C. jejuni with different genomic backgrounds (i.e., C. jejuni NCTC 11168 chloramphenicol-resistant strain and F38011 kanamycin-resistant strain). C. jejuni performed HGT at the frequency of 1027 in Escherichia coli-C. jejuni biofilms, while HGT was not detectable in Salmonella enterica-C. jejuni biofilms. IMPORTANCE Antimicrobial-resistant C. jejuni has been listed as a high priority of public health concern worldwide. To tackle the rapid evolution of AMR in C. jejuni, it is of great importance to understand the extent and characteristics of HGT in C. jejuni biofilms, which serve as the main survival strategy of this microbe in the farm-to-table continuum. In this study, we demonstrated that biofilms significantly enhanced HGT compared to the planktonic state (P,0.05). Biofilm cultivation time and extracellular DNA (eDNA) amount were related to varied HGT frequencies. C. jejuni could spread AMR genes in both monospecies and dual-species biofilms, mimicking the survival mode of C. jejuni in food chains. These findings indicated that the risk and extent of AMR transmission among C. jejuni organisms have been underestimated, as previous HGT studies mainly focused on the planktonic state. Future AMR controlling measures can target biofilms and their main component eDNA. [ABSTRACT FROM AUTHOR]