Characterization of methicillin-resistant and enterotoxins producing Staphylococcus aureus in bovine milk in India

Abstract

The present study was conducted to detect the occurrence of methicillin-resistant and enterotoxin producing Staphylococcus aureus in bovine milk with SCCmec, spa type, antimicrobial sensitivity and MIC of anti-staphylococcal drugs against the isolates. A total of 450 composite milk samples both from cattle with or without mastitis were collected from all agro-climatic zones of West Bengal. Nine (9.6%) S. aureus isolates were phenotypically detected as MRSA and all of them possessed mecA. Whereas, 12 (12.8%) and 4 (4.3%) isolates possessed the staphylococcal enterotoxins sei and seg, respectively. Six and three isolates belonged to SCCmec type Iva and type V, respectively. Spa typing of the isolates showed MRSA isolates belonged to t304 and t6297. All the MRSA isolates were multidrug resistant. The MIC of oxacillin, vancomycin, ampicillin, ciprofloxacin and linezolid against MRSA isolates was 8->256 μg ml−1, 0.064–0.256 μg ml−1, 0.38–2 μg ml−1 and 6–8 μg ml−1, and 0.1 μg ml−1, respectively. The finding is worrying from public health point of view due to detection of MRSA and enterotoxin (seg,sei) producing S. aureus in milk samples which are commonly associated with human infection or food poisoning cases. This is the first comprehensive study with substantial numbers of samples for characterization of MRSA in bovine milk in India.