Title:
Adaptive acid tolerance response of Vibrio parahaemolyticus as affected by acid adaptation conditions, growth phase, and bacterial strains.

Abstract:
Vibrio parahaemolyticus strain 690 was isolated from gastroenteritis patients. Its thermal and ethanol stress responses have been reported in our previous studies. In this study, we further investigated the effects of various acid adaptation conditions including pH (5.0-6.0) and time (30-90 min) on the acid tolerance in different growth phases of V. parahaemolyticus 690. Additionally, the adaptive acid tolerance among different V. parahaemolyticus strains was compared. Results indicated that the acid tolerance of V. parahaemolyticus 690 was significantly increased after acid adaptation at pH 5.5 and 6.0 for 30-90 min. Among the various acid adaptation conditions examined, V. parahaemolyticus 690 acid-adapted at pH 5.5 for 90 min exhibited the highest acid tolerance. The acid adaptation also influenced the acid tolerance of V. parahaemolyticus 690 in different growth phases with late-exponential phase demonstrating the greatest acid tolerance response (ATR) than other phases. Additionally, the results also showed that the induction of adaptive ATR varied with different strains of V. parahaemolyticus. An increase in acid tolerance of V. parahaemolyticus was observed after prior acid adaptation in five strains (556, 690, BCRC 13023, BCRC 13025, and BCRC 12864), but not in strains 405 and BCRC 12863.