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This project is designed to better understand the characteristics of different L. monocytogenes subtypes and to gain a better understanding of which specific L. monocytogenes subtypes cause human disease and how these types differ from those that cannot cause human disease. We will comprehensively characterize L. monocytogenes isolates from humans, animals and foods using both DNA fingerprinting methods and methods for evaluating a strain's ability to cause disease. This work will ultimately contribute to the development of science-based food safety regulations that economically meet public health needs.
Listeria monocytogenes is a bacterium capable of causing a serious foodborne disease ("listeriosis") in humans. A 1998-9 listeriosis outbreak in the US affected more than lOO people and killed at least 20 people. An estimated 1,700 cases of human listeriosis occur annually in the U.S. About 20-40% of people infected with this bacterium die. Only a few, genetically distinctive L. monocytogenes subtypes appear to be responsible for most listeriosis cases, suggesting that not all subtypes are equally capable of causing human foodborne disease. L. monocytogenes is commonly present in the environment; thus preventing contamination of food products with this organism is challenging. In fact, most food recalls due to bacterial contamination are a consequence of the presence of L. monocytogenes. Current regulations require the recall of any ready-to-eat food containing more than one L. monocytogenes cell/25 g. Therefore, L. monocytogenes contamination presents a serious economic concern to food processors.