Listeria monocytogenes is an important food-borne pathogen responsible for approximately 500 deaths annually in the United States and its presence in foodstuffs has resulted in a number of extensive food recalls. Not all strains of L. monocytogenes are equally capable of causing disease in humans and animals.  For example, during an epidemic outbreak some strains will cause severe disease while other co-disseminated strains do not appear to cause any disease.

Therefore, determining what makes epidemic strains of L. monocytogenes virulent is critically important to devising improved detection, subtyping, and intervention methods and strategies. Our group recently identified a group of epidemic strains of L. monocytogenes that are more infective in an oral mouse challenge model compared with their environmental counterparts. One explanation for this difference is that epidemic strains are better able to withstand exposure to low pH and bile encountered in the gastrointestinal tract as compared to most environmental strains. In this study we are using whole genome expression arrays to identify genes that are differentially expressed under acid or bile stress and to determine if gene expression differs between epidemic and environmental strains. These experiments will involve a collection of 13 previously characterized epidemic and environmental strains and the resulting study would identify transcriptional signatures that distinguish these two groups under defined stress conditions.

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Food and Waterborne Diseases Integrated Research Network

National Institute of Allergy and Infectious Diseases 6610 Rockledge Drive, MSC 6612 Bethesda, MD 20892-6612

National Institutes of Health (NIH) 9000 Rockville Pike Bethesda, Maryland 20892

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