99D-8 |
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H.-J. E. PANG and K. R. Matthews. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, 65 Dudley Rd., New Brunswick, NJ 08901-8520 Listeria monocytogenes, a psychrotrophic pathogen, is responsible for listeriosis and has the highest mortality rate among foodborne pathogens. In this study, L. monocytogenes serotypes 4b, 1/2a and 1/2b of human origin were exposed to food matrices (chocolate milk, hot dog slurry and nutrient media) to test the hypothesis that exposure to food matrix (at 4oC) and temperature abuse impacts their virulence. Two objectives were initiated to address the hypothesis: 1) Development of a novel system for exposure of bacteria to food matrices; 2) Determine infectivity and virulence of L. monocytogenes that were recovered from the novel exposure system using an in vitro Caco-2 cell assay. Using dialysis, this novel exposure system closely simulated abuse of cells in a food matrix using dialysate from each of the food matrices described previously. This system also facilitated the ease of recovery of bacterial cells for the further investigation of their virulence potential using the in vitro Caco-2 cell assay. Growth characteristics of L. monocytogenes showed no notable differences in isolates cultured in whole food systems versus their corresponding food dialysates. At 4h, 12h, and 24h, populations were approximately 103, 107, and 109 CFU/ml for chocolate milk, hotdog slurry, or nutrient medium, respectively. L. monocytogenes exposed to chocolate milk or hot dog slurry at 4oC showed similar efficiency for entry (at levels 105 CFU/ml). Populations increased approximately 2-log during the intracellular multiplication phase of the assay. Results of the virulence assay suggests that exposure of L.monocytogenes to food matrices and the subsequent temperature abuse has little or no effect on the ability of the pathogen to enter, replicate within, and kill Caco-2 cells. Growth studies suggest that the novel dialysis system is an appropriate surrogate for food matrices used in the present study.
Session 99D, Food Microbiology: General
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