Investigation of Bacillus cereus contamination sites in a dairy plant with RAPD-PCR

The usefulness of RAPD-PCR as a typing method for investigation of Bacillus cereus isolates from a dairy plant was evaluated. A 1-d in-depth sampling study along the entire production line was performed and long-term sampling of products was conducted over two years. In addition, farm bulk tank isolates were collected. Isolates from an individual sample during storage at 7°C were often identical. Large clusters of identical isolates were found in the silo tank in the 1-d study and in samples from the long-term study. In combination with analytical data, these results indicated a prolonged contamination problem caused by a mesophilic strain early in the production chain. Detailed and useful information on occurrence of psychrotrophic B. cereus was obtained along the production line and among products. RAPD-PCR appeared to be a useful typing method for B. cereus isolates. In combination with carefully planned sampling and microbiological analysis, RAPD could be helpful in solving dairy contamination problems in pasteurized milk.