Determination of Biofilm Formation, Antibacterial Resistance and Genotypes of Bacillus cereus Isolates from Raw Milk

Bacillus cereus is a foodborne pathogen that has a widespread presence in the environment and frequently found in foods especially in dairy products. Raw milk contaminated with B. cereus could be the cause of its widespreadness in the environment. In this study, it was aimed to determine the genotypes, biofilm formation, antimicrobial susceptibilities, and antibiotypes of B. cereus isolates from raw milk. For this aim, B. cereus isolated and identified from 10 of 250 raw milk samples were investigated. Biofilm forming abilities were determined in vitro by Congo Red Agar Method. Kirby Bauer Disc Diffusion Method was used for determining the antibiotic susceptibilities of the isolates. According to the antibiotic susceptibility results, quantitative antibiotyping was implemented. Genotyping of the isolates were performed by RAPD-PCR. Biofilm formation was determined in 40% of the isolates. The resistances against amoxicillin-clavulanic acid, gentamicin, erythromycin, vancomycin, chloramphenicol, tetracycline, trimethoprim-sulfamethoxazole were determined in 100%, 0%, 30%, 0%, 0%, 0%, and 50% of the isolates, respectively. In the quantitative antibiotyping, the isolates showed similarity between 0.75 to 1.00. The phylogenetic similarities were calculated between 29% to 82%. In conclusion, raw milks might threat the public health because of having potential of containing the antibiotic resistant B. cereus.