Defining the in vivo physiology of E. coli O157:H7 in cattle to improve phage-based interventions

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E. coli O157 is part of a unique group of bacterial pathogens that intimately attach to the outside of host cells as their main colonisation strategy. They employ a type 3 secretion system to inject effector proteins that result in remodelling of the actin cytoskeleton and silencing of innate cellular responses. The bacteria also inhibit host cell apoptosis to keep these 'base camp' cells alive and this is enabled by Shiga toxin which limits local proliferation of new epithelial cells. T3S and intimate attachment are essential for colonisation of the bovine reservoir host and excretion from cattle directly or indirectly can lead to severe human infections. Our grouping has been studying the biology of this zoonotic pathogen in the bovine host for the last two decades and we now want to dissect E. coli O157 gene expression at the main site of colonisation in cattle, the terminal rectum, to advance phage-based interventions. We will carry out RNAseq on O157 sampled from experimentally infected cattle. We will compare this expression with bacteria grown in mucus and intimately attached to cultured bovine epithelial cells. We propose that by understanding the expression 'states' of the bacteria in vivo, it will facilitate selecting bacteriophages active on E. coli O157 when colonising cattle. The second main aim of the research will be defining the bacterial surface receptors used by phage active on E. coli O157 under these specific growth conditions. By combining the expression and phage activity information we will be able to select phage combinations likely to be effective in vivo. The final part of the research will be to test phage formulations in cattle colonised by E. coli O157. An understanding of the in vivo of physiology of this public health threat is important for the design of any cattle-based intervention. The approach being taken to optimise phage treatments in this study can be applied to other important bacterial infections.