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Enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC) are food-borne pathogens that colonize the small intestine and colon, respectively. To cause disease, these pathogens must overcome the action of different host antimicrobial peptides (AMPs) secreted into these distinct niches. We have shown previously that EHEC expresses high levels of the OmpT protease to inactivate the human cathelicidin LL-37, an AMP present in the colon. In this study, we investigate the mechanisms used by EPEC to resist human α-defensin 5 (HD-5), the most abundant AMP in the small intestine. Quantitative PCR was used to measure transcript levels of various EPEC surface structures. High transcript levels of gfcA, a gene required for group 4 capsule (G4C) production, were observed in EPEC, but not in EHEC. The unencapsulated EPEC ∆gfcA and EHEC wild-type strains were more susceptible to HD-5 than EPEC wild-type. Since the G4C is composed of the same sugar repeats as the lipopolysaccharide O-antigen, an -antigen ligase (waaL) deletion mutant was generated in EPEC to assess its role in HD-5 resistance. The ∆waaL EPEC strain was more susceptible to HD-5 than both the wild-type and ∆gfcA strains. The ∆gfcA∆waaL EPEC strain was not significantly more susceptible to HD-5 than the ∆waaL strain, suggesting that the absence of -antigen influences G4C formation. To determine whether the G4C and -antigen interact with HD-5, total polysaccharide was purified from wild-type EPEC and added to the ∆gfcA∆waaL strain in the presence of HD-5. The addition of exogenous polysaccharide protected the susceptible strain against HD-5 killing in a dose-dependent manner, suggesting that HD-5 binds to the polysaccharides present on the surface of EPEC. Altogether, these findings indicate that EPEC relies on both the G4C and the -antigen to resist the bactericidal activity of HD-5. [ABSTRACT FROM AUTHOR]

Shiga toxin-producing Escherichia coli (STEC) strains are commensal bacteria in cattle with high potential for environmental and zoonotic transmission to humans. Although O157:H7 is the most common STEC serotype, there is growing concern over the emergence of more than 200 highly virulent non-O157 STEC serotypes that are globally distributed, several of which are associated with outbreaks and/or severe human illness such as hemolytic-uremic syndrome (HUS) and hemorrhagic colitis. At present, the underlying genetic basis of virulence potential in non-O157 STEC is unknown, although horizontal gene transfer and the acquisition of new pathogenicity islands are an expected origin. We used seropathotype classification as a framework to identity genetic elements that distinguish non-O157 STEC strains posing a serious risk to humans from STEC strains that are not associated with severe and epidemic disease. We report the identification of three genomic islands encoding non-LEE effector (nle) genes and 14 individual nle genes in non-O157 STEC strains that correlate independently with outbreak and HUS potential in humans. The implications for transmissible zoonotic spread and public health are discussed. These results and methods offer a molecular risk assessment strategy to rapidly recognize and respond to non-O157 STEC strains from environmental and animal sources that might pose serious public health risks to humans. [ABSTRACT FROM AUTHOR]

Citrobacter rodentium is a natural pathogen of mice that causes intestinal hyperplasia and colitis. Resistant strains such as C57BL/6J (B6) experience a self-limiting disease that peaks between one and two weeks post infection, followed by a clearing of the infection and complete recovery. However, the inbred mouse strains C3H/HeJ (C3), C3H/HeOuJ (C3Ou) and FVB/N (FVB) are highly susceptible to C. rodentium infection and develop more severe symptoms of disease leading to high rates of mortality during infection. We have recently demonstrated through a systematic genetics approach that a single locus on proximal chromosome 15 is responsible for the susceptibility of both C3 and C3Ou mice to C. rodentium infection. We have named the locus Citrobacter rodentium infection 1 (Cri1). Here we show that Cri1 also controls susceptibility to C. rodentium in FVB mice, using a targeted method of genotyping to stratify (B6 x FVB)F2 mice according to their genotype at Cri1. Mice that inherit two copies of the resistant B6 allele have 97% cumulative survival at day 30 post-infection, whereas those that inherit one or two copies of Cri1 from the FVB parent have significantly lower rates of survival (35% and 42%, respectively). These results provide evidence for a common genetic cause of fatal infectious colitis in C3, C3Ou and FVB mice following infection with Citrobacter rodentium.