Search

Helicobacter pylori causes clinical disease primarily in those individuals infected with a strain that carries the cytotoxin associated gene pathogenicity island (cagPAI). The cagPAI encodes a type IV secretion system (T4SS) that injects the CagA oncoprotein into epithelial cells and is required for induction of the pro-inflammatory cytokine, interleukin-8 (IL-8). CagY is an essential component of the H. pylori T4SS that has an unusual sequence structure, in which an extraordinary number of direct DNA repeats is predicted to cause rearrangements that invariably yield in-frame insertions or deletions. Here we demonstrate in murine and non-human primate models that immune-driven host selection of rearrangements in CagY is sufficient to cause gain or loss of function in the H. pylori T4SS. We propose that CagY functions as a sort of molecular switch or perhaps a rheostat that alters the function of the T4SS and "tunes" the host inflammatory response so as to maximize persistent infection.

Gastric adenocarcinoma is strongly associated with Helicobacter pylori infection; however, most infected persons never develop this malignancy. H. pylori strains harboring the cag pathogenicity island ([cag.sup.+]), which encodes CagA and [...]

Recently, we reported that the type 6 secretion system (T6SS) of Aeromonas hydrophila SSU plays an important role in bacterial virulence in a mouse model, and immunization of animals with the T6SS effector haemolysin co-regulated protein (Hcp) protected them against lethal infections with wild-type bacteria. Additionally, we showed that the mutant bacteria deleted for the vasH gene within the T6SS gene cluster did not express the hcp gene, while the vasK mutant could express and translocate Hcp, but was unable to secrete it into the extracellular milieu. Both of these A. hydrophila SSU mutants were readily phagocytosed by murine macrophages, pointing to the possible role of the secreted form of Hcp in the evasion of the host innate immunity. By using the [DELTA]vasH mutant of A. hydrophila, our in vitro data showed that the addition of exogenous recombinant Hcp (rHcp) reduced bacterial uptake by macrophages. These results were substantiated by increased bacterial virulence when rHcp was added along with the [DELTA]vasH mutant in a septicaemic mouse model of infection. Analysis of the cytokine profiling in the intraperitoneal lavage as well as activation of host cells after 4 h of infection with the [DELTA]vasH mutant supplemented with rHcp indicated that this T6SS effector inhibited production of proinflammatory cytokines and induced immunosuppressive cytokines, such as interleukin-10 and transforming growth factor-[beta], which could circumvent macrophage activation and maturation. This mechanism of innate immune evasion by Hcp possibly inhibited the recruitment of cellular immune components, which allowed bacterial multiplication and dissemination in animals, thereby leading to their mortality. DOI 10.1099/mic.0.041277-0

In this study, we delineated the role of N-acylhomoserine lactone(s) (AHLs)-mediated quorum sensing (QS) in the virulence of diarrhoeal isolate SSU of Aeromonas hydrophila by generating a double knockout [DELTA]ahyRI mutant. Protease production was substantially reduced in the AahyRI mutant when compared with that in the wild-type (WT) strain. Importantly, based on Western blot analysis, the [DELTA]ahyRI mutant was unable to secrete type VI secretion system (T6SS)-associated effectors, namely haemolysin coregulated protein and the valine-glycine repeat family of proteins, while significant levels of these effectors were detected in the culture supematant of the WT A. hydrophila. In contrast, the production and translocation of the type Ill secretion system (T3SS) effector AexU in human colonic epithelial cells were not affected when the ahyRI genes were deleted. Solid surface-associated biofilm formation was significantly reduced in the AahyRI mutant when compared with that in the WT strain, as determined by a crystal violet staining assay. Scanning electron microscopic observations revealed that the [DELTA]ahyRI mutant was also defective in the formation of structured biofilm, as it was less filamentous and produced a distinct exopolysaccharide on its surface when compared with the structured biofilm produced by the WT strain. These effects of AhyRI could be complemented either by expressing the ahyRI genes in trans or by the exogeneous addition of AHLs to the [DELTA]ahyRI/ahy[R.sup.+] complemented strain. In a mouse lethality experiment, 50 % attenuation was observed when we deleted the ahyRI genes from the parental strain of A. hydrophila. Together, our data suggest that AHL-mediated QS modulates the virulence of A. hydrophila SSU by regulating the T6SS, metalloprotease production and biofilm formation. DOI 10.1099/mic.0.031575-0

Deletion of the murein (Braun) lipoprotein gene, Ipp, attenuates the Yersinia pestis CO92 strain in mouse models of bubonic and pneumonic plague. In this report, we characterized the virulence of strains from which the plasminogen activating protease (pla)-encoding pPCP1 plasmid was cured from either the wild-type (WT) or the [DELTA]/pp mutant strain of Y. pestis CO92 in the mouse model of pneumonic infection. We noted a significantly increased survival rate in mice infected with the Y. pestis pPCP-/[DELTA]/pp mutant strain up to a dose of 5000 [LD.sub.50]. Additionally, mice challenged with the [pPCP.sup.-]/[DELTA]/pp strain had substantially less tissue injury and a strong decrease in the levels of most cytokines and chemokines in tissue homogenates and sera when compared with the WT-infected group. Importantly, the Y. pestis [pPCP.sup.-]/[DELTA]/pp mutant strain was detectable in high numbers in the livers and spleens of some of the infected mice. In the lungs of [pPCP.sup.-]/[DELTA]/pp mutant-challenged animals, however, bacterial numbers dropped at 48 h after infection when compared with tissue homogenates from 1 h post-infection. Similarly, we noted that this mutant was unable to survive within murine macrophages in an in vitro assay, whereas survivability of the [pPCP.sup.-] mutant within the macrophage environment was similar to that of the WT. Taken together, our data indicated that a significant and possibly synergistic attenuation in bacterial virulence occurred in a mouse model of pneumonic plague when both the Ipp gene and the virulence plasmid pPCP1 encoding the pla gene were deleted from Y. pestis. DOI 10.1099/mic.0.029124-0

Yersinia pestis is a Gram-negative bacterium, and the causative agent of bubonic plague and pneumonic plague. Because of its potential use as a biological warfare weapon, the plague bacterium has been placed on the list of category A select agents. The dynamics of pneumonic infection following aerosolization of the highly virulent Y. pestis CO92 strain have been poorly studied; therefore, the purpose of this study was to determine the [LD.sub.50] dose, bacterial dissemination, cytokine/chemokine production and tissue damage in Swiss-Webster mice over a 72 h course of infection. We exposed mice in a whole-body Madison chamber to various doses of Y. pestis CO92 aerosolized by a Collison nebulizer, and determined that the [LD.sub.50] presented dose (Dp) of the bacterium in the lungs was 2.1 x [10.sup.3] c.f.u. In a subsequent study, we infected mice at a Dp of 1.3 x [10.sup.4] c.f.u., and harvested organs and blood at 1, 24, 48 and 72 h post-infection. Histopathological examination, in addition to measurement of bacterial dissemination and cytokine/chemokine analysis, indicated progressive tissue injury, and an increased number of animals succumbing to infection over the course of the experiment. Using these data, we were able to characterize the mouse plague model following aerosolization of Y. pestis CO92.

Helicobacter pylori is the strongest risk factor for gastric adenocarcinoma. The H. pylori cancer-associated cag pathogenicity island (cag-PAI) encodes a type IV secretion system (T4SS), which translocates microbial DNA and activates TLR9; however, most cag-PAI+-infected persons do not develop cancer and cag-PAI-independent regulators of pathogenesis, including strain-specific adhesins, remain understudied. We defined the relationships between H. pylori HopQ adhesin allelic type, gastric injury, and TLR9 activation. Type I hopQ alleles were significantly associated with magnitude of injury, cag-T4SS function, and TLR9 activation. Genetic deletion of hopQ significantly decreased H. pylori-induced TLR9 activation, implicating this adhesin in H. pylori-mediated disease. [ABSTRACT FROM AUTHOR]