Prevalence, Cross Contamination, Virulence, and Multidrug Resistance Profiles of <i>Staphylococcus aureus</i> Isolates from Four Middle-Scale Dairy Farms in Bareilly, Northern India

Milk, a nutritious global important food commodity, serves as an excellent medium for microbial growth as well. The foodborne pathogen <i>Staphylococcus aureus</i> is a commensal member of human microflora that enters the food chain through poor hygienic practices and cross contamination and causes various clinical manifestations in humans. During this study, raw milk and swab samples (milker's hand, udder, towel, milking bucket, and farm floor) were collected from four middle-scale buffalo dairy farms. The results revealed <i>S. aureus</i> presence in 11.6% (<i>n</i> = 56/448) bucket raw milk samples and 2.6% (<i>n</i> = 12/448) udder raw milk samples. Contrarily, <i>S. aureus</i> prevalence was significantly higher in farm floors (100%, <i>n</i> = 84/84), towel (35.7%, <i>n</i> = 10/28), milking bucket (11.6%, <i>n</i> = 56/448), milker's hand (10.7%, <i>n</i> = 3/28), and udder swab samples (4.0%, <i>n</i> = 18/448). The chi-square test yielded <i>p</i> values of 0.000, 0.005, and 0.0011 for udder raw milk, udder swab, and milker's hand swab, respectively. The <i>p</i> values of the milking bucket (<i>p</i> = 0.048) and farm floors (<i>p</i> = 0.0183) confirmed their possible role in <i>S. aureus</i> cross contamination. Gene amplifications of nuclease and enterotoxin A indicate potential virulence of <i>S. aureus</i> isolates in collected samples. Antibiotic susceptibility testing revealed multidrug resistance in 44% (<i>n</i> = 239) of <i>S. aureus</i> isolates with the highest resistance of 61% against penicillin. Resistance against ampicillin, streptomycin, and lincomycin was observed. Fewer <i>S. aureus</i> isolates were resistant to kanamycin and erythromycin, whereas the lowest number of resistant isolates was observed against chloramphenicol. A high prevalence of <i>S. aureus</i> in the farm environment and milking equipment suggested the cross contamination of potentially enterotoxin-producing and multidrug-resistant <i>S. aureus</i> to raw milk. Therefore, good hygiene practices should be enforced to avoid foodborne and zoonotic infections.