Nadia Boisen1, Anne-Marie Hansen2, Angela R Melton-Celsa3, Tonia Zangari3, Ninell Pollas Mortensen4, James B Kaper2, Alison D O'Brien3, James P Nataro1. 1. Department of Pediatrics, University of Virginia School of Medicine, Charlottesville. 2. Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore. 3. Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, Maryland. 4. Technology for Industry and the Environment, Discovery-Science-Technology, RTI International, Research Triangle Park, North Carolina Biological and Nanoscale Systems, BioSciences Division, Oak Ridge National Laboratory, Tennessee.
Abstract
BACKGROUND: A Shiga toxin type 2a (Stx2a)-producing enteroaggregative Escherichia coli (EAEC) strain of serotype O104:H4 caused a large outbreak in 2011 in northern Europe. Pathogenic mechanisms for this strain are unclear. We hypothesized that EAEC genes encoded on the pAA virulence plasmid promoted the translocation of Stx2a across the intestinal mucosa. METHODS: We investigated the potential contribution of pAA by using mutants of Stx-EAEC strain C227-11, either cured of the pAA plasmid or deleted for individual known pAA-encoded virulence genes (ie, aggR, aggA, and sepA). The resulting mutants were tested for their ability to induce interleukin 8 (IL-8) secretion and translocation of Stx2a across a polarized colonic epithelial (T84 cell) monolayer. RESULTS: We found that deletion of aggR or aggA significantly reduced bacterial adherence and (independently) translocation of Stx2a across the T84-cell monolayer. Moreover, deletion of aggR, aggA, sepA, or the Stx2a-encoding phage from C227-11 resulted in reduced secretion of IL-8 from the infected monolayer. CONCLUSIONS: Our data suggest that the AggR-regulated aggregative adherence fimbriae I enhance inflammation and enable the outbreak strain to both adhere to epithelial cells and translocate Stx2a across the intestinal epithelium.
BACKGROUND: A Shiga toxin type 2a (Stx2a)-producing enteroaggregative Escherichia coli (EAEC) strain of serotype O104:H4 caused a large outbreak in 2011 in northern Europe. Pathogenic mechanisms for this strain are unclear. We hypothesized that EAEC genes encoded on the pAA virulence plasmid promoted the translocation of Stx2a across the intestinal mucosa. METHODS: We investigated the potential contribution of pAA by using mutants of Stx-EAEC strain C227-11, either cured of the pAA plasmid or deleted for individual known pAA-encoded virulence genes (ie, aggR, aggA, and sepA). The resulting mutants were tested for their ability to induce interleukin 8 (IL-8) secretion and translocation of Stx2a across a polarized colonic epithelial (T84 cell) monolayer. RESULTS: We found that deletion of aggR or aggA significantly reduced bacterial adherence and (independently) translocation of Stx2a across the T84-cell monolayer. Moreover, deletion of aggR, aggA, sepA, or the Stx2a-encoding phage from C227-11 resulted in reduced secretion of IL-8 from the infected monolayer. CONCLUSIONS: Our data suggest that the AggR-regulated aggregative adherence fimbriae I enhance inflammation and enable the outbreak strain to both adhere to epithelial cells and translocate Stx2a across the intestinal epithelium.
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