SubPopulations of Shiga Toxin Producing Escherichia coli: Persistence, Resistance and Pathogenicity

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Experimentalmicrobiology typically assumes bacterial populations are homogenous withrespect to resistance to stress or gene expression. However, in reality purestrain cultures are heterogeneous with a proportion of cells existing in adormant (persistent) state that have enhanced resistance compared to the mainbody of the population. Moreover, dormant cells are missed during culturing asthey either fail or experience delayed growth. In evolutionary terms thepersistent state is a kind of “bet hedging” whereby a proportion of cells willsurvive over extended periods should conditions for the population becomeadverse. To date, the majority of studies relating to persistence has been withrespect to residual populations remaining after antibiotic treatment. Yet,persistence is commonly encountered in the wider environment such as soil, andfood systems, such as foods treated with high pressure processing. Thesignificance of residual populations with respect to food safety is unknownalthough the potential for the re-growth of pathogens or enhanced virulence areboth possibilities. In the proposed research program we will look at thedormant (persistent, VBNC and tolerant) state in Shiga Toxin producingEscherichia coli (STEC) a class of significant clinical and foodbornepathogens. For the first time, the persistent state will be investigated inSTEC and the triggers that both induce or break the dormant state identified.Of relevance will be the regulators of persistence derived from soil microbiotaand rhizosphere that ultimately control pathogen:plant interactions. For thefirst time, it will be demonstrated how prophage influences the persistent stateleading to mutual long term survival of phage and host. Studies of thepersistent state will use state-of-the-art imaging techniques incombination with microfluidics that enable manipulation/ observation at thesingle cell level. Cells in the persistent state will be generated andharvested to facilitate studies on the role of dormancy in resistance to highpressure and lytic phages, in addition to environmental persistence. The impactof the research is potentially wide reaching. From an academic standpointgreater insights into prophage host interactions will be obtained. On anapplication side the research will provide data to assess the food safety risksrepresented by persister cells in the environment and food systems. To date,risk analysis has frequently designated a specified log reduction to verify theefficacy of interventions (for example, pasteurization) without taking intoaccount residual survivors. Although present at low levels, residual survivors could grow during storage or become more virulent within the host. The research will provide data toassess such risks and moreover lead to more effective pathogen controlstrategies through breaking of the dormant state.