Abstract
The survival of bacteria in various environments depends on a number of protective responses including acid tolerance response (ATR). In this study, ATR phenomenon was compared in Salmonella enterica serovar Typhi 6 and Salmonella enterica serovar Typhimurium 98 under different culture conditions. Survival of the adapted culture (preβacid shocked to pH 5.5) was significantly better (p < 0.05) as compared to control, unadapted culture after acid shock at pH 3.3. However, the ATR varied with the serovar, incubation temperature and the growth medium used (all pβvalues < 0.05). S. Typhi 6 failed to grow in pH 3.3 at 45 Β°C. The addition of tetracycline or chloramphenicol (1.0 ΞΌg ml^β1^) to adapted cultures during or after acid shock (pH 3.3) had no effect on ATR expression. In S. Typhimurium 98, growth was increased by 10% or greater in adapted culture (when grown at pH 3.3) as compared to growth observed with an unadapted culture (when grown at pH 7.3) on transfer to fresh growth medium at pH 7.3. A poor ATR observed in nonβgrowing S. Typhimurium 98 suspensions clearly showed that ATR is an energyβconsuming process. Storage of S. Typhimurium 98 cultures in pH 4.5 nutrient broth at 4 Β°C demonstrated that prolonged exposure to acidic conditions is more detrimental in comparison to the cultures stored at pH 7.3 at this temperature. (Β© 2004 WILEYβVCH Verlag GmbH & Co. KGaA, Weinheim)