Thermal Inactivation of Heat-Shocked Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in Dairy Compost

Thermal resistance of heat-shocked Escherichia colt O157 H7. Salmonella, and Listeria monocytogenes was compared with that of non heat-shocked (control) strains in finished dairy compost. A three-strain mixture of each pathogen was heat shocked at 47.5 degrees C for 1 It and inoculated into the compost at a final concentration of 10(7) CFU/g The inoculated compost was placed inside an environmental chamber set at 50, 55, or 60 degrees C with humidity at ca. 70%. The heat-shocked E (coli O157.H7, Salmonella. and L monocytogenes survived better (P < 0 05) at 50 degrees C, with reductions of 2 7. 3.2, and 3 9 log CFU/g within 4 h compared with reductions of 3 6. 4 5. and 5 1 log CFU/g. respectively, in control cultures The heat-shocked cultures of E colt O157.H7. Salmonella. and L monocytogenes had 1 2-. 1.9-. and 2 3-log reductions, respectively, within 1 h at 55 degrees C, whereas the corresponding control cultures had 4-, 5 6-, and 4.8-log reductions, respectively. At 60 degrees C, a rapid population reduction was observed during the come-up time of 14 min in control cultures of E colt O157 H7, Salmonella, and L monocytogenes with 4 9-, 4 8-. and 2.3-log reductions, respectively, compared with 2 6-, 2.4-. 1 7-log reductions, respectively, in heat-shocked cultures. L. monocytogenes,genes survival curves for all three temperatures had extensive tailing, The double Wetbull distribution model was a good fit for the survival curves of pathogens, with differences in the shape parameter of heat-shocked and control cultures. Our results suggest that the heat-shocked pathogens may have extended survival at lethal temperatures attained during the composting process