Prevalence of Bacillus cereus in dairy powders focusing on its toxigenic genes and antimicrobial resistance

Bacillus cereus is a common environmental foodborne microorganism that is mainly found to harbor toxigenic genes with multiple antibiotic resistances and is linked to threatening the safety of dried milk in concern to powdered infant milk formula. In the current investigation, the mean value of B. cereus in 140 samples of powdered milk was 0.57 × 10² ± 0.182 × 10², 0.15 × 10² ± 0.027 × 10², 0.21 × 10² ± 0.035 × 10², and 0.32 × 10² ± 0.072 × 10² CFU/g in a percentage of 64.0 samples of whole milk powder, 43.3 of skim milk powder, 26.7 of powdered infant milk formula and 36.7 milk-cereal-based infant formula, respectively. The results revealed that B. cereus isolates were found to harbor toxigenic genes in the following percentages: 77.8, 2.0, 72.7, 16.2, and 67.7 for nhe, hbl, cytK, ces, and bceT, respectively. Despite all evaluated B. cereus strains were originated from dairy powders, they showed a significant difference (P < 0.05) in their harbored toxigenic cytK gene between whole and skim milk powders with powdered infant formula and milk-cereal-based infant formula, as well as between powdered infant formula and milk-cereal-based infant formula. All isolated B. cereus strains were resistant to cefoxitin, colistin sulfate, neomycin, trimethoprim-sulfamethoxazole, oxacillin, and penicillin. Based on the antimicrobial resistance of B. cereus strains to cephalothin, chloramphenicol, nalidixic acid, and tetracycline, there was a significant difference (P < 0.05) between powdered infant milk formula and whole milk powder strains. This survey is one of few studies proceeded in Egypt to determine the prevalence of toxigenic B. cereus strains in milk-cereal-based infant formula and powdered infant formula as well as skim milk powder.