Characterization of the induction of increased thermotolerance by high osmolarity inSalmonella

Abstract Factors limiting the growth of Salmonella at high temperature were analyzed in minimal medium. The growth of S. typhimurium was curtailed at 44°C by high temperature-dependent block in methionine synthesis. At 45°C, the organism could not grow in glucose-mini- mal medium even with methionine, but growth could be restored at this temperature by the addition of NaCl in the final concentration range of 0.15–0.3 m . Similar results were obtained with two S. enteritidis strains. The growth stimulatory effect of high osmolarity at 45°C was not altered by the osmoprotectant compound glycine betaine. Exposure to 0.3 m NaCl also increased the resistance of S. typhimurium to thermal death at 50°C and to the oxidizing agent H 2 O 2 . However, the high osmolarity-dependent induction of enhanced resistance to 50°C and to H 2 O 2 was completely abolished by glycine betaine. The finding that glycine betaine blocks the induction of resistance to lethal high temperature by high osmolarity could provide a means for enhancing the bactericidal efficacy of heating, because it may be possible to increase the heat sensitivity of contaminating bacteria by supplementing food products with this naturally occurring plant metabolite, prior to thermal processing.