Grants and Contributions:

Grant or Award spanning more than one fiscal year. (2017-2018 to 2022-2023)

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.