BACILLUS CEREUS IN SOME INDIAN FOODS, INCIDENCE AND ANTIBIOTIC, HEAT AND RADIATION RESISTANCE

ABSTRACT Samples of 124 different foods purchased from local markets were examined to determine the incidence of Bacillus cereus. The foods examined were pulses, rice and rice products, oils, fish, meat, spices, milk and milk products and ice creams. Isolations were made on mannitol‐egg yolk‐polymyxin B agar medium and confirmed by morphological and biochemical tests. B. cereus was present in 28.5% of rice and rice products (100% of boiled rice), 40% of fish, 80% of chicken and meat products, 30% of spices and 87% of ice creams. Pasteurized milk and milk products and protein‐rich food powders containing milk or cocoa were also contaminated with B. cereus. The average count of B. cereus varied from 2 × 102 to 5 × 105/g. The response of cells and spores from 6 randomly selected isolates of B. cereus to antibiotics and to heat treatment was identical. However, both vegetative and spore forms of these isolates exhibited subtle differences in radiation resistance. Pathogenicity of all isolates was determined by their ability to lyse human erythrocytes. Five of the six isolates selected produced a strong nonhemolytic toxin which is lethal to mice.