Chromosomal and plasmid DNA mediated antibiotic resistance among Staphylococcus aureus obtained from mastitic milk of cattle in Jaipur, Rajasthan

The present investigation was aimed to isolate and identify the Staphylococcus aureus isolates from mastitic milk sample of cattle along with studies of phenotypic and genotypic antibiotic resistance pattern. Among 100 mastitic milk samples of cattle, total 20 (20.0%) isolates were identified and confirmed as S. aureus. Out of the total identified isolates, 17 (85.0%) isolates having multidrug resistance (MDR) property including 11 (55.0%) isolates had 0.2 or more than 0.2 MAR index value with high-risk potential source of spread MDR. In antibiotic sensitivity studies, Gentamicin, Doxycycline Hydrochloride and Tetracycline antibiotics were most effective with 85.0%, 65.0% and 60.0% efficacy, respectively while highest resistance was recorded against Penicillin–G (80.0%). In reference to specific resistance mechanisms, six (30.0%) isolates were detected as MRSA and one (C58) isolate had High- level mupirocin resistance. None of the isolate was detected as VRSA along with average 1.37mcg/ml MIC for vancomycin. Both chromosomal as well as plasmid DNA were evaluated for detection of antibiotic resistance genes i.e. eighteen isolates (90.0%) were carrying blaZ gene (517bp) in chromosomal DNA, while twelve isolate (60.0%) having same gene in plasmid DNA. Only one (C69) isolate was positive for mecA (533bp) gene in both chromosomal and plasmid DNA and none of the isolate was found positive for vanA (560bp) and vanX (480bp) gene.