Listeria monocytogenes (L. monocytogenes) is a Gram-positive pathogenic organism and the causative agent of human and animal listeriosis.... Show moreListeria monocytogenes (L. monocytogenes) is a Gram-positive pathogenic organism and the causative agent of human and animal listeriosis. Listeriosis is a gastrointestinal or invasive systemic illness resulting from consumption of contaminated food products, mainly cheese, deli meats, and fresh produce, by L. monocytogenes. In recent years, several foodborne outbreaks have been reported that were associated with fresh produce, such as cantaloupe, celery and sprouts. Temperature is considered a major factor that affects L. monocytogenes growth during storage. The proliferation of L. monocytogenes varies on different produce items based on storage temperature. In this study, the persistence and population dynamics of three L. monocytogenes strains, LS806 (cheese isolate), LS810 (cantaloupe isolate) and LS808 (celery isolate) were evaluated by incubating inoculated fresh-cut green bell pepper and red bell pepper at various temperatures (5oC, 10oC, and 25oC) for 14 days. To assess the risk of L. monocytogenes in these fresh-cut vegetable items, a primary predictive model was fitted for L. monocytogenes growth data using DMFit. Green bell pepper had significantly (P<0.05) higher pH and aw, and higher amounts of yeast and mold and Enterobacteriaceae than did red bell pepper. In green bell pepper, all three strains showed no significant difference (P>0.05) in growth rate when incubated at the same temperature. In red bell peppers, LS808 had the highest (P<0.05) growth rate at both 5°C and 25°C out of the three strains. All of the three strains grew significantly faster (P<0.01) at 25°C than either 5°C or 10°C in both green and red bell peppers. All three strains obtained less than 1 log10 growth increase after incubating at 25°C for 6 hours on pre-chilled produce. Some strains (LS806 and LS810) significantly increased (P<0.01) during two 5-hour 25°C incubations, but did not reach 1 log10 growth increase. The results indicate that L. monocytogenes not only persists, but also grows in chopped green and red bell peppers at 5, 10, and 25°C, and strains grew faster at the higher temperature (25°C). Data obtained could be further evaluated for determining whether Time/temperature control for safety (TCS) designation should be applied to chopped green and red bell peppers. M.S. in Food Safety and Technology, July 2015 Show less
