ISOLATION, IDENTIFICATION AND CHARACTERIZATION OF BACILLUS-CEREUS FROM THE DAIRY ENVIRONMENT

In order to determine the major contamination sources of milk with (ps ychrotrophic) Bacillus cereus, the incidence of vegetative cells and s pores of B. cereus on dairy farms, at two dairy processing plants and in pasteurized milk in household refrigerators was investigated. On da iry farms the major contamination sources were soil and faeces. In win ter, when the cows were housed, used bedding probably also participate s in this contamination route. The udder will be contaminated, finally resulting in the presence of B. cereus in raw milk. The organism coul d be detected in 35% of the raw milk samples analyzed. During procesin g, and increase in the percentage of positive samples was observed. Th ese results suggest that B. cereus can be introduced via sources other than raw milk; equipment may play an important role in this. Biochemi cal and molecular typing showed that selection of strains takes place in the milk production chain. It was demonstrated that some types were found in the raw milk, during processing and in the end products, ind icating that raw milk is an important source of contamination. Other t ypes could only be detected after the pasteurization step in the produ ction process supporting the assumption that additional contamination occurs during processing. If stored under proper conditions, maximum s torage temperature 7 degrees C, and consumed within the expiry date, t he levels of B. cereus in pasteurized milk will, in general, not excee d 10(5) per ml and cause no problems for healthy adults.