Mozliwosc wzrostu Bacillus cereus wyizolowanych z mleka i jego produktow w niskiej temperaturze

The aim of this study was to identify the psychrotrophic Bacillus cereus strains in raw milk, in the environment of milk production and in chosen dairy products, as well as to examine the ability of the selected strains to grow in milk in lower temperatures. The study was conducted in 2 stages. At the first stage 821 strains were analyzed. They had been isolated from the following specimens: soil (29 strains), cow faeces (221), forage (90), the surface of teats (142), the surface of milking cups (38), raw milk (152), pasteurized milk (33) and mould cheese (116). All the analyzed strains were psychrotrophic (a growth in 6.5°C, over 10 days). At the second stage of the study 35 B. cereus strains, isolated form raw milk and the environment of milk production, were analyzed. It was observed that those strains have an ability to grow in milk stored at the temperature of 4°C, 6°C and 8°C over 7 days. The psychrotrophic features were observed in 3% of the strains isolated from the surface of the milking cups, 3% - cow faeces, 7% - soil, 7% - forage, 25 % - raw milk, 12% - pasteurized milk and 17% - mould cheese. The growth of 5.7%, 11.4% and 45.7% strains respectively was noted in the milk stored in the temperatures of 4°C, 6°C and 8°C. The highest permissible temperature for the storage of pasteurized milk in Poland are: 8°C in trade and 6°C in transport. However, these temperatures are not low enough to guarantee product safety, because the growth of the psychrotrophic B.cereus strains is possible in such conditions.