Understanding and exploiting the response of EHEC O157:H7 to human gastrointestinal chemical signals

Abstract

Enterohemorrhagic Escherichia coli (EHEC) is a clinically relevant foodborne pathogen, resulting in over 95,000 cases of EHEC-associated illness and 60 deaths each year in the US alone. Since EHEC is a continuous global issue with new outbreaks constantly occurring, the development of new therapeutic strategies is vital to minimizing the cases of infection seen each year. A key aspect in new drug development is the identification of vulnerabilities in EHEC’s pathogenicity, in particular, during its transit through the human gastrointestinal (GI) tract. As EHEC passes through the human GI tract to its site of colonization in the large intestine, it faces a multitude of host assaults including acute acid stress in the stomach, bile salt stress and cationic antimicrobial peptide exposure in the small intestine, and short chain fatty acid (SCFA) stress in the large intestine. The research carried out in this doctoral dissertation focuses on understanding how EHEC senses chemical cues from the host’s innate immune responses and how this knowledge can be exploited to develop effective antimicrobial strategies. Our findings successfully demonstrate that a novel antimicrobial peptide ameliorates infection in a mouse model of infection by enhancing acid-induced pathogen killing during gastric passage, and that the DNAbinding protein, Dps, plays a significant role in protecting EHEC against peptide killing. Moreover, this research successfully shows that varying concentrations of SCFAs result in differential modulation of EHEC virulence – a finding that contributes to our understanding of the role of diet and commensal flora in host susceptibility to infection. Together the findings of this research demonstrate how the selected innate host defences throughout the human GI tract can be exploited and/or manipulated to effectively prevent infection by the human pathogen EHEC.