Incidence and properties of Bacillus cereus strains from a milk powder plant - risk consideration and quality assurance.

Bacillus (B.) cereus is known as a pathogenic microorganism causing infecti on and intoxication. The occurrence in milk powder is of particular interes t due to its use as basic material for, e.g., infant formulae. In a large milk powder plant, 146 B. cereus-strains (10.7%) were isolated f rom 1365 milk powder samples, and 183 (85.1%) from 215 environmental sample s. All strains were characterized by bacteriological methods. Additionally, production of toxin was examined with a commercial test kit and a cell cul ture model. Selected groups of strains were typed by application of a RAPD- PCR method. In the frame of epidemiological tracing, the results from bacte riological and molecular typing were used for cluster analysis to detect si milarities between strains. However, no similarities were detected, neither between strains from milk powder or from environmental samples, nor betwee n these groups of strains. Thus it was confirmed that there was a daily inp ut of B. cereus in the dairy via raw milk. In cell culture, toxin formation was detected in 85.4% of the strains. Via test kit, even in 97.9%. The col lected data were used in the discussion on risk assessment in the sense of consumer protection, and on demands for a quality assurance (QA) concept. A contamination of milk powder and subsequent products cannot be avoided. Ne vertheless, the colony counts expected under good production practice are m uch lower than the counts mentioned in literature to be hazardous to human health (about 10(4)/ml or g). The input of about 1 spore/ml via raw milk co rresponds to the findings of 1 - 10 spores/ml in milk powder when consideri ng a concentration factor of 10. This spore count is only reached under opt imal hygienic production conditions, effectively suppressing multiplication of B. cereus. For a monitoring of hygienic production conditions a referen ce value of max. 10 spores/g would be appropriate. The aim of modern consumer policy should be to inform consumers about the h ealth risk incurred by B. cereus, and about the measures how to preserve qu ality and shelf life of a product.