SummaryWe discovered a new small non-coding RNA (sRNA) gene, vrrA of Vibrio cholerae O1 strain A1552. A vrrA mutant overproduces OmpA porin, and we demonstrate that the 140 nt VrrA RNA represses ompA translation by base-pairing with the 5Ј region of the mRNA. The RNA chaperone Hfq is not stringently required for VrrA action, but expression of the vrrA gene requires the membrane stress sigma factor, s E , suggesting that VrrA acts on ompA in response to periplasmic protein folding stress. We also observed that OmpA levels inversely correlated with the number of outer membrane vesicles (OMVs), and that VrrA increased OMV production comparable to loss of OmpA. VrrA is the first sRNA known to control OMV formation. Moreover, a vrrA mutant showed a fivefold increased ability to colonize the intestines of infant mice as compared with the wild type. There was increased expression of the main colonization factor of V. cholerae, the toxin co-regulated pili, in the vrrA mutant as monitored by immunoblot detection of the TcpA protein. VrrA overproduction caused a distinct reduction in the TcpA protein level. Our findings suggest that VrrA contributes to bacterial fitness in certain stressful environments, and modulates infection of the host intestinal tract.
Vibrio cholerae is the causal bacterium of the diarrheal disease cholera, and its growth and survival are thought to be curtailed by bacteriovorous predators, e.g., ciliates and flagellates. We explored Caenorhabditis elegans as a test organism after finding that V. cholerae can cause lethal infection of this nematode. By reverse genetics we identified an extracellular protease, the previously uncharacterized PrtV protein, as being necessary for killing. The killing effect is associated with the colonization of bacteria within the Caenorhabditis elegans intestine. We also show that PrtV is essential for V. cholerae in the bacterial survival from grazing by the flagellate Cafeteria roenbergensis and the ciliate Tetrahymena pyriformis. The PrtV protein appears to have an indirect role in the interaction of V. cholerae with mammalian host cells as judged from tests with tight monolayers of human intestinal epithelial cells. Our results demonstrate a key role for PrtV in V. cholerae interaction with grazing predators, and we establish Caenorhabditis elegans as a convenient organism for identification of V. cholerae factors involved in host interactions and environmental persistence.cholera ͉ host interactions ͉ environmental persistence C holera continues to be a major public and individual health problem, especially in those regions of the world where it is endemic. Colwell (1) first hypothesized that coastal waters were an important reservoir of Vibrio cholerae. Huq et al. (2) reported that V. cholerae O1 cells could be observed to be attached to a variety of phytoplankton and zooplankton species. The incidence and severity of epidemics have been linked to salinity, water temperature, turbidity, and plankton blooms (3, 4). Cholera epidemics occur in a regular seasonal pattern. It has been suggested that during interepidemic periods V. cholerae exists in an unexplained ecological association with aquatic organisms (5). During the environmental phase, V. cholerae resides in diverse aquatic environments, often in association with marine plankton (6). The association of V. cholerae with zooplankton has proven to be a key factor in deciphering the global nature of cholera epidemics (7). In such natural bacterioplankton communities V. cholerae and other bacteria are also at the base of the pelagic microbial food web (8). Bacterial growth and survival are subject to constraint by bacteriovorous predators, e.g., protozoa such as ciliates and flagellates (9, 10). Little has been known about mechanisms and adaptations of bacteria to reduce grazing mortality compared with adaptations toward abiotic factors (substrate, temperature, pH, etc.) (11).V. cholerae expresses well characterized factors to establish and cause disease in the mammalian host, including cholera toxin (CT) and toxin-coregulated pili (Tcp). It has been shown that quorum sensing (QS) plays a role in the regulation of virulence in V. cholerae (12). At least three autoinducer signaling circuits function through the action of LuxO, leading to the repression of...
BackgroundBackground: Cytolethal distending toxin (CDT) is one of the well-characterized virulence factors of Campylobacter jejuni, but it is unknown how CDT becomes surface-exposed or is released from the bacterium to the surrounding environment.ResultsOur data suggest that CDT is secreted to the bacterial culture supernatant via outer membrane vesicles (OMVs) released from the bacteria. All three subunits (the CdtA, CdtB, and CdtC proteins) were detected by immunogold labeling and electron microscopy of OMVs. Subcellular fractionation of the bacteria indicated that, apart from the majority of CDT detected in the cytoplasmic compartment, appreciable amounts (20-50%) of the cellular pool of CDT proteins were present in the periplasmic compartment. In the bacterial culture supernatant, we found that a majority of the extracellular CDT was tightly associated with the OMVs. Isolated OMVs could exert the cell distending effects typical of CDT on a human intestinal cell line, indicating that CDT is present there in a biologically active form.ConclusionOur results strongly suggest that the release of outer membrane vesicles is functioning as a route of C. jejuni to deliver all the subunits of CDT toxin (CdtA, CdtB, and CdtC) to the surrounding environment, including infected host tissue.
. The most prevalent adhesin was that encoded by the iha gene (91%; 127 of 139 strains), which was distributed in all seropathotypes. toxB and efa1 were present mainly in strains of seropathotypes A and B, which were LEE positive. saa was present only in strains of seropathotypes C, D, and E, which were LEE negative. Two fimbrial genes, lpfA O157/OI-141 and lpfA O157/OI-154 , were strongly associated with seropathotype A. The fimbrial gene lpfA O113 was present in all seropathotypes except for seropathotype A, while sfpA was not present in any of the strains studied. The distribution of STEC adhesins depends mainly on serotypes and not on the source of isolation. Seropathotype A, which is associated with severe disease and frequently is involved in outbreaks, possesses a unique adhesin profile which is not present in the other seropathotypes. The wide distribution of iha in STEC strains suggested that it could be a candidate for vaccine development.
Here we report a loop-mediated isothermal amplification (LAMP) method for detecting Shigella and enteroinvasive Escherichia coli. The target for this LAMP method is the ipaH gene which is carried by both of the pathogens. The LAMP method efficiently detected the gene within 2 h at a minimal amount of bacteria (8 CFU) per reaction.
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