Adkins, B. | bioRxiv Science

bioRxiv2018

CexE Is A Virulence Factor of Citrobacter rodentium And Present In Enteric Pathogens Of Humans

CexE is a 12 kDa protein that was originally reported to be present in just three strains of enterotoxigenic Escherichia coli (ETEC); a frequent causes of diarrheal illnesses worldwide. However, an examination of recently sequenced genomes has revealed that CexE is actually present in a majority of ETEC strains. Homologs of CexE are also present in enteroaggregative E. coli (EAEC) and other enteric pathogens including Yersinia enterocolitica, Providencia alcalifaciens, and Citrobacter rodentium. CexE and its homologs are expressed within virulence regulons of ETEC, EAEC, and C. rodentium. This, along with its distribution across several species of enteric pathogens, suggest that CexE confers a selective advantage to these pathogens. However, this hypothesis has yet to be tested in vivo. Here we demonstrate that CexE is conditionally secreted to the external leaf of the outer membrane of ETEC. Although CexE does not appear to play a role in adherence in vitro, it does facilitate colonization of murine intestinal tissues by C. rodentium in vivo. In adult mice wild-type bacteria reached significantly higher loads and were shed in higher numbers than a cexE::kan mutant. A similar trend was observed in neonatal mice. In addition, all of the neonates infected with the wild-type strain succumbed to infection within 16 days of inoculation. In contrast, 45% of the neonates infected with the cexE::kan strain survived for the 30 day duration of the experiment. These finding indicate that CexE is a conditionally secreted virulence factor that increases the colonization of hosts by enteric pathogens.

microbiology↗

bioRxiv2017

The eIF2α Kinase Heme Regulated Inhibitor (HRI) Protects The Host From Infection By Regulating Intracellular Pathogen Trafficking

Phosphorylation of eIF2 by its kinases is a stress response universally conserved among the eukaryota. Previously, we reported that the eIF2 kinases Heme Regulator Inhibitor (HRI) and Protein Kinase R (PKR) control distinct activities of diverse bacterial pathogens. Specifically for Listeria monocytogenes, it was shown that in HRI-deficient cells there was a reduction in the translocation of the pathogen to the cytosolic compartment as well as reduced loading of pathogen-derived antigens on MHC-1 complexes. Here we show that Hri -/- mice, as well as wild-type mice treated with a HRI inhibitor, are more susceptible to listeriosis. In the first few hours of L. monocytogenes infection, Hri -/- mice supported greater pathogen proliferation in the liver compared to that observed in Hri +/+ mice. This greater susceptibility of Hri -/- mice was not due to deficits in immune cell development as proportions and numbers of innate and adaptive cell compartments were largely normal and these mice could mount potent antibody responses to a model T cell-dependent antigen. Using in vitro cellular infection assays, we show that the rate of pathogen efflux from infected Hri -/- macrophages and fibroblasts is significantly higher than that observed in infected Hri +/+ cells. In contrast to the stark differences between Hri +/+ and Hri -/- cells in the infection dynamics of virulent L. monocytogenes, HRI was entirely dispensable for killing non-virulent strains of L. monocytogenes. These results suggest that in wild-type cells, HRI helps ensure the cellular confinement of virulent L. monocytogenes and loading of cytosolic-derived antigens on MHC-1 complexes that limit pathogen spreading and activating innate immune responses, respectively.

immunology↗