The effect of salt concentration and pH on the heat resistance of Escherichia coli in typtic soy both

Oulkheir, S. and Ounine, Khadija and Elhaloui, N. E. and Douira, A. and Ikko, Latifa and Bricha, Saadia and Attarassi, B. (2007) The effect of salt concentration and pH on the heat resistance of Escherichia coli in typtic soy both. Acta Microbiologica et Immunologica Hungarica, 54 (4). pp. 399-412. ISSN 1217-8950

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Abstract

The effect of the acid and the osmotic stress on the heat resistance of Escherichia coli (EC1 and EC2) was studied at 63 °C in tryptic soy broth adjusted to various pHs (2.5, 4.5 and 6) and various NaCl concentrations (2, 4 and 8%). In the second study, the effect of pretreatment on thermotolerance of E. coli cells was determined.The heat resistance of both strains was low at pH 2.5, but strain EC1 was more resistant than strain EC2. On the contrary, the heat resistance increased with increasing the pH values. Addition of NaCl (2%) to TSB medium, was involved in the protection of cells against heat inactivation, this protective effect was, however, not observed by increasing the NaCl concentration up to 8%.The combined effect of the pH and NaCl on the thermal resistance of both strains was significantly lower at pH 2.5 and NaCl 8%, the number of viable cells decreased from approximately 108 CFU/ml to an undetectable number within 20 min for strain EC1 and 15 min for strain EC2, respectively.This study indicates that heat resistance of strain EC1 was enhanced after acid or thermal adaptation. Heat resistance of strain EC2 was, however, enhanced only after thermal adaptation. For both strains no relationship was found between salt adaptation and the ability to resist thermal stress.

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