The effect of acid adaptation on the susceptibility of Bacillus cereus to the stresses of temperature and H2O2 as well as enterotoxin production.

In the present study, Bacillus cereus 1-4-1, which is capable of causing diarrheal syndrome, was subjected to acid adaptation at pH 5.5 for 2 hours. The effect of acid adaptation on the survival of B. cereus subjected to subsequent lethal challenges at both low (4 degrees and -18 degrees C) and high temperatures (49 degrees C) as well as in the presence of 5 mM H(2)O(2) was investigated. Additionally, enterotoxin production by B. cereus as influenced by acid adaptation was examined. Results revealed that acid adaptation increased the survival of B. cereus during storage at -18 degrees C while a decreased survival was noted for the acid-adapted cells during storage at 4 degrees C. In addition, the acid-adapted cells were less susceptible to high temperature than the nonadapted cells. On the other hand, acid adaptation did not change the susceptibility of test organism to H(2)O(2). It was also found that acid adaptation time affected the enterotoxin production of B. cereus cells. The 1- to 2-hour acid-adapted cells exhibited a reduced level of enterotoxin production while cells acid adapted for 4 hours and the nonadapted cells showed no difference in the level of enterotoxin production. Besides, the acid-adapted cells showed a reduced lag period for growth and enterotoxin production when they were grown in tryptic soy broth.