Ethanol and NaCl susceptibility and protein expression of acid-adapted B. cereus 1-4-1 as well as its growth patterns in the presence of various carbon and nitrogen sources.

In the present study, the foodborne pathogen Bacillus cereus 1-4-1 was subjected to acid adaptation treatment by suspending the test organism in tryptic soy broth (pH 5.5) for 2 hours. The susceptibility of the acid-adapted and nonadapted cells of B. cereus 1-4-1 to high concentrations of ethanol (20%) and NaCl (20%) was then examined. In addition, the effect of acid adaptation on the protein expression profile of B. cereus 1-4-1 as well as the growth patterns of the acid-adapted and nonadapted cells of the test organism in the presence of various carbon and nitrogen sources were compared. Results revealed that acid-adapted B. cereus 1-4-1 was more susceptible to ethanol (20%) and NaCl (20%) than its nonadapted counterpart. Analysis with one-dimensional SDS-PAGE showed no distinct difference in the expression of the 16 proteins bands noted in the nonadapted cells compared with those of acid-adapted cells. Two-dimensional electrophoresis revealed that the acid adaptation treatment affected the expression of 26 species of protein, with the levels of 12 proteins increasing and 14 proteins decreasing in the cells of acid-adapted B. cereus 1-4-1 compared with those of the control cells. Furthermore, immunoblotting detected GroEL-like protein with a similar level in the acid-adapted and nonadapted cells of B. cereus 1-4-1 while failing to find the presence of a DnaK-like protein. B. cereus 1-4-1, regardless of acid adaptation, exhibited the highest maximum growth with sucrose as the carbon source while the maximum growth was found in the presence of either peptone, soytone, tryptone, or yeast extract as the nitrogen source, with these showing no significant difference. Finally, the growth patterns of the acid-adapted and nonadapted cells were similar.