The incidence of Bacillus cereus in foods in Central Thailand.

Thirty of 53 different raw and cooked or processed foods obtained in Central Thailand were demonstrated to contain Bacillus cereus. The level of contamination was found to depend on the type of food sampled; the mean was 3.2 X 10(6) organisms/gm on raw and cooked or processed foods ready for consumption, and 2.8 X 10(8) organisms/gm on cooked or processed foods kept overnight at kitchen temperature. B. cereus was commonly found on rice (both uncooked and boiled or fried), dried chilli pepper, shrimp paste, and on certain kinds of cooked foods seasoned with these products. Most of the total of 275 B. cereus isolates were found to possess biochemical reactions typical for B. cereus. Variations were also examined among several isolates. Nineteen per cent of the isolates did not produce acid from salicin. Certain types of the food tested were also demonstrated by volunteer experiments to carry enterotoxigenic B. cereus.