IDENTIFICATION OF CONTAMINATION SOURCES OF BACILLUS-CEREUS IN PASTEURIZED MILK

Ln order to determine the sources of Bacillus cereus in pasteurized mi lk, a total of 232 milk samples from various sampling points along mil k processing lines and 122 environmental swabs were collected in two d airy plants between March and September, 1996. The incidence of B. cer eus vegetative cells in raw milk from the plants was low (less than or equal to 10%). However, the incidence and the average counts of B. ce reus spores in the raw milk were very high and similar to those of B. cei-eus vegetative cells in pasteurized milk or final products after e nrichment (> 80% and 1.1 X 10(5) cfu ml(-1), respectively). The incide nce and average count of both vegetative cells and spores of B. cereus in environmental swabs was low. Using the microbial idendification sy stem (MIDI), a library of B. cereus fatty acid profiles comprising 229 B. cereus isolates from milk samples and environmental swabs was cons tructed using a critical Euclidian distance of 6.0 units as the cut-of f value. Using this library, the relationship between 546 B. cereus is olates from the different sampling points along the milk processing li nes and the environmental swabs was determined. Most B. cereus isolate s obtained from the pasteurized mill; and final products belonged to t he same sub-groups as the B. cereus strains germinated from spores in raw milk. Furthermore, specific sub-groups were found in pasteurized m ilk, different dairy plants and at different sampling times. The resul ts suggested that B. cereus spores in raw milk were the major source o f B. cereus in pasteurized milk and that post-pasteurization contamina tion along the milk processing lines was possibly a minor source of B. cereus in pasteurized milk. (C) 1998 Elsevier Science B.V. All rights reserved.