THE ROLE OF HEAT-EXCHANGERS IN THE CONTAMINATION OF MILK WITH BACILLUS-CEREUS IN DAIRY PROCESSING PLANTS

In the dairy industry microbiological contamination may arise from equ ipment used for handling or processing. In this study it was demonstra ted that Bacillus cereus spores could adhere to stainless steel, germi nate and/or multiply in a tube heat exchanger. The levels of B cel eus detected in the tubes, after 24 h at 20 degrees C, varied from less t han 1 to 2600 cm(-2). Adhering cells and/or spores were more resistant to cleaning with K500 and sodium hydroxide, determined by laboratory suspension tests and surface tests on stainless steel. This was confir med in afield trial with a tube heat exchanger; after cleaning B cereu s could still be isolated from all tubes determined by swab samples of individual tubes. The identity of the isolates was checked by polymer ase chain reaction/randomly amplified polymorphic DNA typing to confir m that the organisms found on the surfaces were the same as the bacter ia in the ingoing milk.