Occurrence and characterization of (psychrotrophic) Bacillus cereus on farms in The Netherlands
1996
Giffel, M.C. te | Beumer, R.R. (Wageningen Agricultural Univ. (Netherlands). Lab. of Food Microbiology) | Slaghuis, B.A. | Rombouts, F.M.
In order to determine the major contamination sources of raw milk with (psychrotrophic) Bacillus cereus, the incidence of B. cereus spores and vegetative cells on farms in the Netherlands was investigated. Samples were taken from air, soil, grass, bedding, feed, drinking water, faeces, udders and milk. Some biochemical and growth characteristics of the strains isolated were examined. In total 847 presumptive B. cereus colonies were isolated from all sources examined. The levels present in the various samples ranged from less than 10 up to 10 exp 7 per g or ml for vegetative cells and less than 10 to 10 exp 5 per g or ml for spores. According to the ISO confirmation tests and/or the carbohydrate patterns (API 50 CHB), 766 (90 percent) of these isolates were confirmed to be B. cereus. The major contamination sources of B. cereus were soil and faeces. In winter when cows are housed, used bedding probably also participates in this contamination route. The udder will be contaminated, finally resulting in the presence of these organisms in raw milk. About 40 percent of the isolated strains showed growth at 7degree C and were considered to be psychrotrophic. Of the strains isolated from raw milk 30 percent were able to arow at 7degree C. The presence of psychrotrophic spores in raw milk will lead to their presence in pasteurized milk due to heat-resistance properties. Since at low storage temperatures these psychrotrophs will germinate, grow and subsequently spoil the product faster than mesophilic types, the psychrotrophic strains will have a more significant impact on the keeping quality of milk.
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