title: Cold shock induction of thermal sensitivity in Listeria monocytogenes.
abstract: Cold shock at 0 to 15 degrees C for 1 to 3 h increased the thermal sensitivity of Listeria monocytogenes. In a model broth system, thermal death time at 60 degrees C was reduced by up to 45% after L. monocytogenes Scott A was cold shocked for 3 h. The duration of the cold shock affected thermal tolerance more than did the magnitude of the temperature downshift. The Z values were 8.8 degrees C for controls and 7.7 degrees C for cold-shocked cells. The D values of cold-shocked cells did not return to control levels after incubation for 3 h at 28 degrees C followed by heating at 60 degrees C. Nine L. monocytogenes strains that were cold shocked for 3 h exhibited D(60) values that were reduced by 13 to 37%. The D-value reduction was greatest in cold-shocked stationary-phase cells compared to cells from cultures in either the lag or exponential phases of growth. In addition, cold-shocked cells were more likely to be inactivated by a given heat treatment than nonshocked cells, which were more likely to experience sublethal injury. The D values of chloramphenicol-treated control cells and chloramphenicol-treated cold-shocked cells were no different from those of untreated cold-shocked cells, suggesting that cold shock suppresses synthesis of proteins responsible for heat protection. In related experiments, the D values of L. monocytogenes Scott A were decreased 25% on frankfurter skins and 15% in ultra-high temperature milk if the inoculated products were first cold shocked. Induction of increased thermal sensitivity in L. monocytogenes by thermal flux shows potential to become a practical and efficacious preventative control method.
authors.affiliation: Microbial Food Safety Research Unit, Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Wyndmoor, Pennsylvania 19038, USA. amiller@cfsan.fda.gov
authors.forename: A J
authors.initials: AJ
authors.lastname: Miller
authors.forename: D O
authors.initials: DO
authors.lastname: Bayles
authors.forename: B S
authors.initials: BS
authors.lastname: Eblen
mesh_terms: D000818:Animals; D002417:Cattle; D002645:Chickens; D003080:Cold Temperature; D006358:Hot Temperature; D008087:Listeria / Q000302:isolation & purification / Q000502:physiology; D008089:Listeria monocytogenes / Q000254:growth & development / Q000302:isolation & purification / Q000502:physiology*; D008460:Meat / Q000382:microbiology*; D011200:Poultry; D013045:Species Specificity; D013552:Swine; D013997:Time Factors