Foodborne pathogens continue to pose a potential food safety hazard in ready-to-eat (RTE) meat. Chlorine is commonly used to sanitize processing equipment where Escherichia coli O157:H7 (Ec) may survive and contaminat...Foodborne pathogens continue to pose a potential food safety hazard in ready-to-eat (RTE) meat. Chlorine is commonly used to sanitize processing equipment where Escherichia coli O157:H7 (Ec) may survive and contaminate food products. The objective of this study was to characterize the survival behavior of Ec with different stresses on RTE meats. A multi-strain cocktail of Ec was pre-treated with freezing shock for 15 - 20 h and/or chlorine (0, 25, and 50 ppm) for one hour, and then inoculated onto RTE meat surfaces to obtain about 3.0 log CFU/g. Samples were stored at three abuse temperatures (12℃, 18℃, and 24℃) and Ec was enumerated during the storage. The freezing shock impact was studied using the Ec cocktail stored in a freezer overnight followed by chlorine exposure for one hour. The lag phase and growth rate of Ec were estimated using DMFit (Combase, Baranyi’s model). Results indicated that Ec growth was suppressed by chlorine treatment. Freezing shock was found to have little impact in terms of lag time and growth rate. The lag phase of Ec after exposure to 0 ppm of chlorine (50.3 h) was shorter than that of Ec treated with 25 ppm (54.6 h) and 50 ppm (164.1 h) at 12℃. However, the lag phase decreased with an increase in temperature, e.g. at 25 ppm, lag times were 54.6, 51.1 and 48.9 h for 12℃, 18℃ and 24℃, respectively. Lag times increased with an increase in chlorine concentration. At 24℃, lag times were 15.8, 48.9, and 52.4 h for 0, 25, and 50 ppm, respectively. The growth rate increased with an increase in temperature for 0 and 25 ppm chlorine levels, but decreased at 50 ppm level. Growth rate and lag phase as a function of temperature and chlorine concentration can be described by polynomial models and modified Ratkowsky-type and Zwietering-type models. Results of this study will contribute to risk assessment of RTE meats.展开更多
This study aimed to determine the antibiotic and bacteriocin sensitivity of Listeria monocytogenes strains isolated from animal derived foods. With disc diffusion assay, all fourteen L. monocytogenes strains were susc...This study aimed to determine the antibiotic and bacteriocin sensitivity of Listeria monocytogenes strains isolated from animal derived foods. With disc diffusion assay, all fourteen L. monocytogenes strains were suscepti-ble to the antibiotics, including penicillin G, vancomycin, tetracycline, chloramphenicol, rifampicin, erythromycin, gentamicin and trime- thoprim. However, the percentages of fosfomycin and streptomycin resistances were 92.9% and 7.1%, respectively. Multiple resistances were not observed among the tested strains. The results of well diffusion assays showed that all strains were inhibited by the cell-free supernatant of a bacteriocin-producing strain, Pediococcus acidilactici 13, with the inhibition zones ranging from 16.00 to 24.50 mm. These results provide useful information on antibiotic resistance of L. monocytogenes strains isolated from foods, and can potentially be used to develop bacteriocin-based interventions to guard against the hazards associated with L. monocytogenes in ready-to-eat meat and poultry products.展开更多
文摘Foodborne pathogens continue to pose a potential food safety hazard in ready-to-eat (RTE) meat. Chlorine is commonly used to sanitize processing equipment where Escherichia coli O157:H7 (Ec) may survive and contaminate food products. The objective of this study was to characterize the survival behavior of Ec with different stresses on RTE meats. A multi-strain cocktail of Ec was pre-treated with freezing shock for 15 - 20 h and/or chlorine (0, 25, and 50 ppm) for one hour, and then inoculated onto RTE meat surfaces to obtain about 3.0 log CFU/g. Samples were stored at three abuse temperatures (12℃, 18℃, and 24℃) and Ec was enumerated during the storage. The freezing shock impact was studied using the Ec cocktail stored in a freezer overnight followed by chlorine exposure for one hour. The lag phase and growth rate of Ec were estimated using DMFit (Combase, Baranyi’s model). Results indicated that Ec growth was suppressed by chlorine treatment. Freezing shock was found to have little impact in terms of lag time and growth rate. The lag phase of Ec after exposure to 0 ppm of chlorine (50.3 h) was shorter than that of Ec treated with 25 ppm (54.6 h) and 50 ppm (164.1 h) at 12℃. However, the lag phase decreased with an increase in temperature, e.g. at 25 ppm, lag times were 54.6, 51.1 and 48.9 h for 12℃, 18℃ and 24℃, respectively. Lag times increased with an increase in chlorine concentration. At 24℃, lag times were 15.8, 48.9, and 52.4 h for 0, 25, and 50 ppm, respectively. The growth rate increased with an increase in temperature for 0 and 25 ppm chlorine levels, but decreased at 50 ppm level. Growth rate and lag phase as a function of temperature and chlorine concentration can be described by polynomial models and modified Ratkowsky-type and Zwietering-type models. Results of this study will contribute to risk assessment of RTE meats.
文摘This study aimed to determine the antibiotic and bacteriocin sensitivity of Listeria monocytogenes strains isolated from animal derived foods. With disc diffusion assay, all fourteen L. monocytogenes strains were suscepti-ble to the antibiotics, including penicillin G, vancomycin, tetracycline, chloramphenicol, rifampicin, erythromycin, gentamicin and trime- thoprim. However, the percentages of fosfomycin and streptomycin resistances were 92.9% and 7.1%, respectively. Multiple resistances were not observed among the tested strains. The results of well diffusion assays showed that all strains were inhibited by the cell-free supernatant of a bacteriocin-producing strain, Pediococcus acidilactici 13, with the inhibition zones ranging from 16.00 to 24.50 mm. These results provide useful information on antibiotic resistance of L. monocytogenes strains isolated from foods, and can potentially be used to develop bacteriocin-based interventions to guard against the hazards associated with L. monocytogenes in ready-to-eat meat and poultry products.
