Thermotolerance of Listeria monocytogenes and Salmonella typhimurium after sublethal heat shock

Abstract

The effect of prior heat shock on thermotolerance of Listeria monocytogenes and Salmonella typhimurium in broth culture was determined. Bacteria were grown at the permissive temperature of 35°C, sublethally heated at 35 (control), 42, 48, and 52°C (nonpermissive control) for various times, and inactivated at either 57.8 or 52°C. The induction of increased thermotolerance by heat shock, although consistent within each experiment, was generally not significant for L. monocytogenes; the increase was significant for S. typhimurium. Temperature shift experiments with L. monocytogenes suggested that induced thermotolerance was not long lived unless the shock temperature was maintained. Exposure to temperatures above the range for normal cell growth (the normal of Arrhenius range) (13) leads to progressive loss of bacterial viability. When bacteria are shifted for a short period from lower to higher temperatures within or slightly above their normal growth range, a degree of protection against the lethal effects of a subsequent shift to a higher temperature or an acquired thermotolerance is achieved (17,20,26).Several investigators (20, 29) concluded that acquired thermotolerance develops during the brief incubation period at elevated but nonlethal temperature as a result of heat shock response, i.e., induction of a specific set of proteins known as heat shock proteins that mediate recovery to stress-induced damage (16,20,26). A direct cause-and-effect relationship between heat shock protein synthesis and acquired thermotolerance, however, is controversial (23, 26).The effect of heat shock response on food safety may be important because certain foods are thermally processed to ensure safety (11). Mackey and Derrick (17, 18) pioneered such studies with Salmonella spp. in broth, liquid whole egg, and reconstituted dried milk and concluded that marginal heat treatments may not be adequate in certain instances. Recent foodborne outbreaks of listeriosis were epidemiologically linked to the consumption of dairy products and meats; hence, the thermal processing parameters of these foods are being reexamined (5,8). This study was undertaken to determine the degree of acquired thermotolerance conferred on Listeria monocytogenes and Salmonella typhimurium by heat shock response and the kinetics and duration of its induction.(Results of this study were presented at the 12th Food Microbiology Research Conference, Chicago, Ill., 8 to 12 November 1989.) L. monocytogenes F5069 was obtained from Robert Weaver, Centers for Disease Control, Atlanta, Ga. This strain belongs to serotype 4b and was isolated from raw bovine milk (3, 4). S. typhimurium 42ScBs was obtained from J. G. Bradshaw, Food and Drug Administration, Cincinnati, Ohio. The strain was isolated from 2% lowfat milk, epidemiologically linked to the 1983 Chicago milk outbreak, and carries the outbreak strain plasmid profile (22).

INHIBITION OF SALMONELLA TYPHIMURIUM ON POULTRY BY THE LACTOPEROXIDASE SYSTEM1

“…1990). The heat shock proteins appear to increase D values of S. fyphirnuriurn 1 to 2 fold (Mackey and Derrick 1986;Bunning et al 1990). Although we did not analyze for heat shock proteins, their presence may indicate why more than a 5 rnin treatment was needed at 60C to decrease S. typhirnuriurn counts.…”

“…It has been shown that heat treatments, such as immersion of carcasses in hot water, poultry carcasses (Dawson et al 1963;Klose and Bayne 1971;Cox et al 1974b: Thomson et al 1976; Thomson et al 1979;Morrison and Fleet 1985). Other end-product treatments which have been proposed for reducing or eliminating salmonellae from poultry carcasses include spray rinsing , air scrubbing (Dikens and Cox 1992), gamma irradiation (Mulder et al 1977, Katta et al 1991, immersion in chlorinated water (Mead et al 1975;Thomson et al 1976) and solutions of various chemicals such as organic acids (Lillard et al 1987;Cox et al 1974a;Juven et al 1974), gluteraldehyde (Thomson et al 1977), sorbates (To and Robach 1980), and trisodium phosphate (Bender 1992).…”

Modelling the effect of the redox potential and pH of heating media onListeria monocytogenesheat resistance

“…To have additional margin of safety, combined action of different environmental factors such as pH, water activity, temperature, food composition and physiological state of vegetative cells and spores were studied recently (Knabel et al 1990;Casadei et al 1998;Gnanou Besse et al 2000;Tienungoon et al 2000;Koutsoumanis and Sofos 2005;Fernandez et al 2007;Leguerinel et al 2007). Mathematical models have been proposed to describe and quantify the impact of these environmental factors on L. monocytogenes inactivation resulting from NaCl and temperature treatments (Bunning et al 1990;Linton et al 1992;Membre et al 1997;Augustin et al 1998), pH, NaCl and lactic acid treatments (Tienungoon et al 2000), and modification of water activity (Fernandez et al 2007).…”

Effect of environmental stresses on the sensitivity ofEnterobacter sakazakiiin powdered infant milk formula to gamma radiation

“…E. sakazakii in PIMF could be expected to have been exposed to environmental stresses such as starvation, desiccation and temperature extremes or to different types of detergents and sanitizers in processing plants. Since stress can influence bacterial response to lethal physical treatment (Bunning et al 1990;Leenanon and Drake 2001), it seemed appropriate to consider whether environmental history (prior stress) could influence the irradiation resistance of E. sakazakii.…”