Identification and characterization of novel genetic factors contributing to the significance of Listeria monocytogenes as a foodborne pathogen

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The perils of pathogen-contaminated food are fresh in the minds of many Canadians, and stem from the recent outbreak linked to widespread distribution of E. coli O157:H7 contaminated beef products across North America. Correspondingly, consequences of food safety failures are of considerable interest to Canadians. Regarding Listeria monocytogenes (Lm), 99% of listeriosis cases are estimated to derive from contaminated food. Therefore, improved mitigation strategies aimed at more effective control of Lm are required to reduce recalls and rates of listeriosis. To this end, my research program aims to identify factors contributing to food chain survival that enable more effective Lm mitigation. At this time, we are focusing on a recently discovered genomic island (LGI1) reported in deli meat and BC seafood. This islet encodes putative stress response, quaternary ammonium compound resistance, and virulence genes. Notably, strains carrying LGI1 were recently shown to form a new epidemic clone (ECV), and have caused human disease in Canada since 1988. To elucidate whether LGI1 genes contribute to food chain survival and/or virulence, my research program will use traditional and molecular approaches to address hypotheses. In short, we will compare Lm 1/2a serotype strains lacking LGI1 to 1/2a strains possessing LGI1 to see if differences exist in the ability to tolerate food-related stress (acidic pH, high salt) and sanitizers. Similarly, we will determine if Lm having LGI1 adhere to food surfaces and enterocytes more effectively. To complement these traditional food microbiology approaches, my program will also use qPCR and targeted gene deletion/complementation to confirm LGI1 contributions. As well, since LGI1 encodes an alternate sigma factor and a two-component regulator, RNA sequencing will be employed to investigate possible stress response/regulatory differences in strains encoding LGI1. This research program will contribute new knowledge regarding the role of LGI1. Considering its association with clinical listeriosis in Canada, such insight is critical, and will provide a foundation from which new and/or improved control strategies will evolve.