Abstract
Factors limiting the growth ofSalmonellaat high temperature were analyzed in minimal medium. The growth ofS. typhimuriumwas 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 0.15–0.3m. Similar results were obtained with twoS. enteritidisstrains. The growth stimulatory effect of high osmolarity at 45°C was not altered by the osmoprotectant compound glycine betaine. Exposure to 0.3mNaCl also increased the resistance ofS. typhimuriumto thermal death at 50°C and to the oxidizing agent H2O2. However, the high osmolarity-dependent induction of enhanced resistance to 50°C and to H2O2was 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.
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