The present investigation was carried out to study the vancomycin resistance pattern of Staphylococcus aureus isolates (n = 274) obtained from 352 milk samples of bovine (269) and caprine (63) clinical and subclinical mastitis from different districts of West Bengal, India. Of them, seven isolates (vancomycin-resistant S. aureus [VRSA] 1-7) exhibited resistance to vancomycin. Minimum inhibitory concentration of vancomycin (MIC) for VRSA2 and VRSA3 was ≥16 μg/ml; thus categorized as VRSA. For rest of the isolates, MIC was 8 μg/ml and they were grouped as vancomycin intermediate S. aureus (VISA). Even though all the isolates were resistant to cefoxitin and oxacillin and possessed mecA gene, none of them carried vancomycin resistance gene. Furthermore, all the seven isolates were subjected to Staphylococcal cassette chromosome mec (SCCmec) typing, Staphylococcal protein A (spa) typing, and enterobacterial repetitive intergenic consensus polymerase chain reaction. All the isolates except VRSA3 and VRSA4 from Kolkata district exhibited diverse genetic lineage, irrespective of their host and antibiotic resistance pattern. These two isolates showed clonal similarity (MRSA-SCCmec-V-spa t267) with methicillin-resistant S. aureus (MRSA) strains previously reported in human and animal infection. Isolation of VRSA and VISA could probably be due to intensive use of vancomycin in healthcare premises, which might have led to the development of glycopeptide-resistant strains and thereafter, further disseminated in the environment, including livestock farms. Detection of VRSA in milk is a serious concern as it may further cause health problems in the consumers. This is the first ever report of VRSA in food animals, even though the pathogen is otherwise prevalent in humans.

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Emergence of antimicrobial resistance among bovine mastitis pathogens is the major cause of frequent therapeutic failure and a cause of concern for veterinary practitioners. This study describes intra-mammary infection of methicillin-resistant Staphylococcus epidermidis (MRSE), methicillin-resistant Staphylococcus aureus (MRSA) and extended spectrum β-lactamase (ESBL) producing Escherichia coli in two Holstein Friesian crossbred cows with subclinical mastitis and one non-descript cow with clinical mastitis in two different districts of West Bengal, India. In total, three MRSE, one MRSA and three ESBL producing E. coli were isolated from these cases. Both the crossbreds were detected with MRSE (HFSE1 and HFSE2) and ESBL producing E. coli (HFEC1 and HFEC2), whereas, simultaneous infection of three pathogens viz. MRSA (NDSA1), MRSE (NDSE1) and ESBL producing E. coli (NDEC1) was found in the non-descript cow. The methicillin-resistant isolates possessed mecA gene and exhibited resistance to various antibiotics such as amikacin, tetracycline and glycopeptides. The ESBL producers were positive for blaCTX-M and blaTEM genes; in addition, HFEC1 and HFEC2 were positive for blaSHV and possessed the genes for class I integron (int1), sulphonamide resistance (sul1), quinolone resistance (qnrS) and other virulence factors (papC, iucD and ESTA1). All the ESBL producers exhibited resistance to a variety of antibiotics tested including third- and fourth-generation cephalosporins and were also intermediately resistant to carbapenems. This is the first ever report on simultaneous occurrence of MRSE, MRSA and ESBL producing E. coli in bovine mastitis indicating a major concern for dairy industry and public health as well.

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