Antibiotic Resistance Studies in Staphylococcus spp Isolated from Bovine Milk

Ten samples of raw milk and 10 samples of pasteurized milk samples were collected from Puducherry and Cuddalore. After collection of samples, in case of raw milk, bacterial pre-enrichment was performed in 90ml of Tryptic Soy Broth with 10ml of raw milk sample and in case of pasteurized milk, pre-enrichment was performed in 90ml of tryptic soy broth with 10ml of pasteurized milk sample. After Pre-enrichment, isolation and identification of the target organism, Staphylococcus spp was carried out. The pre-enriched raw milk and pasteurized milk samples were streaked onto Baird Parker agar plate and Mannitol salt agar plates. Then they were incubated at 37℃ for 24-48hrs. Staphylococcus spp was identified by the yellow colour colonies in Mannitol Salt agar, If Baird Parker agar plate contains black colonies, they were considered as positive for Staphylococcus spp. The isolates were sub cultured to get pure culture. The isolates were identified based on morphological and biochemical characterization. The antibiotic susceptibility testing was carried out for the isolates against the selected antibiotics ampicillin, tetracycline, kanamycin, erythromycin, methicillin, streptomycin, amikacin, gentamicin, ciprofloxacin and chloramphenicol. Among the ten raw milk isolates and ten pasteurized milk isolates, raw milk isolate RMS 9 showed resistance towards six selected antibiotics. RMS 9 isolate was identified by 16S r RNA sequencing. Blast analysis was carried out and the isolate was confirmed as Staphylococcus aureus with similarity percentage of 99.92%. The isolate was submitted in the GEN bank with the accession number OR244369