Enterotoxigenic profile, antimicrobial susceptibility, and biofilm formation of Bacillus cereus isolated from ricotta processing

Sources of Bacillus cereus contamination in a ricotta processing plant were evaluated. In addition, the enterotoxigenic potential, antimicrobial susceptibility, and biofilm formation of the isolates were verified. B. cereus was detected in raw materials, environmental samples (mould, press, storage box, packaging table, and whey sewage drain), and product. From a total of 42 B. cereus isolates, 38.1% and 92.9% were positive for the haemolysin BL and non-haemolytic enterotoxin gene complexes, respectively. All isolates were resistant to ampicillin, penicillin, and trimethoprim; 9.5% were resistant to erythromycin. B. cereus formed a biofilm after 4 d at 25 °C and after 1 d at 39 °C, with counts of 5.0 and 5.1 log cfu cm−2, respectively. During biofilm maturation, an increase in the number of B. cereus spores occurred. However, the biofilm was not formed over 8 d of incubation at 7 °C as the B. cereus isolates were not psychrotrophic.