The members of the Bacillus cereus group are commonly present contaminants of fresh and heat-treated milk.

To determine the level of milk contamination by Bacillus cereus sensu lato, 44 samples were collected from a dairy farm and two independent dairies in northeastern Poland. A total of 680 B. cereus sensu lato isolates were recovered. Based on spore counts, their highest level in milk was found during the spring and summer months. Although significant variations in chromosomal DNA polymorphisms among B. cereus sensu lato isolates were noted based on repetitive element sequence polymorphism (rep-PCR) and pulse-field gel electrophoresis (PFGE), indistinguishable B. cereus isolates were observed in all sampling points and locations. Both B. cereus sensu stricto/Bacillus weihenstephanensis and Bacillus thuringiensis cultured from milk harbored nheA, hblA, and cytK in, respectively, 80%, 55%, and 60% of the isolates. With respect to Bacillus mycoides/Bacillus pseudomycoides, 30% and 70% of theses isolates harbored, respectively, nheA and hblA. The presence of cytK was not detected in any isolate. Our data show the occurrence of potentially toxic B. cereus s.l. in both raw and heat-treated milk, thus emphasizing the requirement for precautions that prevent spore germination and vegetative proliferation by keeping the milk at low temperatures during all steps of production and dispensation to the consumers.