Survival and inactivation of Listeria monocytogenes, shiga toxin-producing Escherichia coli, and multidrug-resistant and susceptible Salmonella serovars exposed to heat and antimicrobials on food contact and food surfaces.

摘要

Compared to planktonic cells, bacterial biofilms are more resistant to sanitizing agents, causing crucial challenges for their inactivation in various food environments. The first study of this dissertation investigated biofilm formation of seven pathogenic Escherichia coli serogroups (i.e., O157, O26, O45, O103, O111, O121, O145) and two or three phenotypes of Salmonella Newport and S. Typhimurium (i.e., susceptible, multidrug-resistant [MDR], and/or multidrug-resistant with acquired ampC gene [MDR-AmpC]).;The second study of this dissertation compared the lactic acid resistance of individual strains of six serogroups of wild-type and rifampicin resistant non-O157 shiga toxin-producing Escherichia coli and susceptible, multidrug-resistant (MDR), and/or MDR with acquired ampC gene (MDR-AmpC) Salmonella Newport and Typhimurium against E. coli O157:H7 (5-strain mixture).;The third study of this dissertation investigated decontamination of beef trimming inoculated with shiga toxin-producing Escherichia coli and Salmonella using lactic acid (LA). The efficacy of LA was compared against (i) six non-O157 Shiga toxin-producing E. coli (nSTEC) serogroups and (ii) antibiotic susceptible and multidrug resistant S. Newport and S. Typhimurium serovars. The antimicrobial effects against these pathogens were compared to those obtained against E. coli O157:H7.;The fourth study of this dissertation was conducted with the objective of evaluating survival and multiplication of L. monocytogenes inoculated on cooked chicken breasts which were stored aerobically at 7°C for 7 days. Reduction of pathogen cells by microwave, domestic oven, and stove top reheating was also evaluated.;The last study of this dissertation was designed to evaluate growth of L. monocytogenes inoculated on cooked chicken meat with different marinades and survival of the pathogen as affected by microwave oven reheating during aerobic storage at 7°C. Raw chicken breast meat samples were treated with three commercially-formulated and three domestically-available marinades, and then cooked (74.4°C internal temperature), cooled to 4°C, and surface-inoculated with L. monocytogenes. During storage at 7°C, on days 0, 1, 2, 4, and 7, samples were reheated by microwave oven (1100 W) for 45 or 90 s and analyzed microbiologically. L. monocytogenes counts on non-marinated control samples increased P<0.05) from 2.7±0.1 to 6.9±0.1 log CFU/g during storage. At day-7 of storage, pathogen levels on samples marinated with tomato juice were not different P&