Incidence and biochemical characteristics of Bacillus flora in Sardinian dairy products

This study was planned to assess the frequency and level of Bacillus spp. contamination in Sardinian dairy products and to evaluate some food-spoilage-related characteristics of the strains isolated. Of the 378 dairy products tested, 265 (70%) were found to contain Bacillus spp. The overall level of contamination ranged from less than 10 cfu per ml or gram up to a maximum of 1200 cfu. A total of 483 strains, belonging to 14 species, have been isolated from the 265 positive samples. The most frequently isolated psychotropic species were B. cereus (18.6% of total isolates), B. coagulans and B. mycoides. B. subtilis, B. licheniformis and B. pumilis were the most common mesophilic strains and B. stearotermophilus was the dominant thermophilic species. Most strains showed strong enzymatic activity, as indicated by the high percentage of isolates capable of hydrolysing casein, gelatin, starch and liquids. As regards possible health hazards, 72% of the B. cereus strains tested showed evidence of toxin production using a reversed passive latex agglutination assay.