Identification of blaVIM, blaIMP and blaSPM-1 Metallo-β-Lactamase Genes in Bacillus subtilis Strains Isolated From Raw Milk and Cheese Samples

Studies on bacterial resistance to common antibiotics are often based on bacteria isolated from patients, with less attention towards foodborne bacteria. This study aimed to investigate the antibiotic resistance pattern and the presence of metallo-β-lactamase (MBL) genes viz blaVIM, blaIMP, and blaSPM-1, in the Bacillus subtilis strains isolated from raw milk and cheese samples. A total of 100 raw milk and cheese samples (50 of each) were collected from the centers of production and distribution of dairy products in Ardabil city in 2017. Bacillus subtilis colonies susceptible to antibiotics were identified by conventional methods. Kirby-Bauer method was used to measure the antibiotic susceptibility and MBL E-test technique was used for detecting MBL enzymes. Presence of blaVIM, blaIMP, and blaSPM-1 MBL genes in the bacterial strains was investigated using PCR. The results showed that 25 (59.52%) isolates from raw milk samples and 16 (43.24%) isolates from cheese samples produced MBL enzyme. The MBL-producing isolates exhibited high level (100%) of antibiotic resistance, except for cefixime (67.40%) and cefotaxime (64.60%). All MBL-producing isolates expressed blaVIM gene, while blaIMP and blaSPM-1 genes were not detected. Based on our results, molecular detection of MBL genes can be used as a complementary method along with common phenotypic diagnostic methods in the samples of dairy products, tested positive for MBL.