Virulence Mechanisms of Listeria Monocytogenes

APPROACH: Wild type and mutant strains of L. monocytogenes will be grown in bacteriological broth. Log-phase organisms will be inoculated intragastrically into A/J mice, a susceptible mouse strain. Mice will be euthanized at various time points and select tissues will be removed for bacteriological and histopathological evaluation of the severity of the infection. We also will evalaute the ability of the wild type and mutant strains for their ability to invade and multiply within intestinal epithelial and fibroblast cell lines. Those strains that differ from the wild type will also be evaluated for prior growth on ready to eat meat products vs. in bacteriological broth and their subsequent effect on virulence.
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PROGRESS: 2003/09 TO 2005/09<BR>
Progress Report Objectives (from AD-416) The objective of this cooperative research project is to identify and evaluate virulence determinants of the foodborne pathogen Listeria monocytogenes that influence its virulence in the gastrointestinal tract. This information will help us to better understand how Listeria monocytogenes causes disease following its ingestion on contaminated food products. Approach (from AD-416) Wild type and mutant strains of L. monocytogenes will be grown in bacteriological broth. Log-phase organisms will be inoculated intragastrically into A/J mice, a susceptible mouse strain. Mice will be euthanized at various time points and select tissues will be removed for bacteriological and histopathological evaluation of the severity of the infection. We also will evalaute the ability of the wild type and mutant strains for their ability to invade and multiply within intestinal epithelial and fibroblast cell lines. Those strains that differ from the wild type will also be evaluated for prior growth on ready to eat meat products vs. in bacteriological broth and their subsequent effect on virulence. Significant Activities that Support Special Target Populations 1935-41420-012-04G - This report serves to document research conducted under a General Assistance type of agreement between ARS and University of Wisconsin. Understanding the risk of foodborne pathogens includes knowing conditions that cause the expression of virulence factors in food. Researchers at the University of Wisconsin in Madison, WI and the ARS Eastern Regional Research Center in Wyndmoor, PA are developing reporter strains of pathogenic E. coli O157:H7 that can be used to measure the expression of virulence factors under real food handling conditions. The enterohemorroghic pathogen Escherichia coli O157:H7 is a major food safety concern due to its ubiquitous presence in cattle products, its low infection dose, and its ability to cause lethal hemolytic uremic syndrome in susceptible target populations. To understand better the status of virulence gene expression in this pathogen while they are embedded into the food matrix, several reporter constructs are used to reveal the promoter activity of key regulator genes and virulence determinants. We have made significant progress in constructing derivatives of a strain of E. coli O157:H7 that will express target genes that are readily observable in a food system, namely luciferase and chloramphenicol acetyl transferase reporters systems. This research supports the Project Plan by enhancing information provided by predictive models that are used in food safety management. The monitoring activities included phone calls and receipt of written reports.