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

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Experimental*microbiology typically assumes bacterial populations are homogenous with*respect to resistance to stress or gene expression. However, in reality pure*strain cultures are heterogeneous with a proportion of cells existing in a*dormant (persistent) state that have enhanced resistance compared to the main*body of the population. Moreover, dormant cells are missed during culturing as*they either fail or experience delayed growth. In evolutionary terms the*persistent state is a kind of “bet hedging” whereby a proportion of cells will*survive over extended periods should conditions for the population become*adverse. To date, the majority of studies relating to persistence has been with*respect to residual populations remaining after antibiotic treatment. Yet,*persistence is commonly encountered in the wider environment such as soil, and*food systems, such as foods treated with high pressure processing. The*significance of residual populations with respect to food safety is unknown*although the potential for the re-growth of pathogens or enhanced virulence are*both possibilities. In the proposed research program we will look at the*dormant (persistent, VBNC and tolerant) state in Shiga Toxin producing*Escherichia coli (STEC) – a class of significant clinical and foodborne*pathogens. For the first time, the persistent state will be investigated in*STEC and the triggers that both induce or break the dormant state identified.*Of relevance will be the regulators of persistence derived from soil microbiota*and rhizosphere that ultimately control pathogen:plant interactions. For the*first time, it will be demonstrated how prophage influences the persistent state*leading to mutual long term survival of phage and host. Studies of the*persistent state will use state-of-the-art imaging techniques in*combination with microfluidics that enable manipulation/ observation at the*single cell level. Cells in the persistent state will be generated and*harvested to facilitate studies on the role of dormancy in resistance to high*pressure and lytic phages, in addition to environmental persistence. The impact*of the research is potentially wide reaching. From an academic standpoint*greater insights into prophage host interactions will be obtained. On an*application side the research will provide data to assess the food safety risks*represented by persister cells in the environment and food systems. To date,*risk analysis has frequently designated a specified log reduction to verify the*efficacy of interventions (for example, pasteurization) without taking into*account 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 to*assess such risks and moreover lead to more effective pathogen control*strategies through breaking of the dormant state.******