Antimicrobial Resistance and Virulence Factors of Staphylococcus aureus in Dairy Farms: Insights from the Animal-Human-Environment Interface

In India, dairy farming is run by medium, small, and landless farmers and has a stable biotope at the animal-human-environment interface. Hence a cross-sectional study was conducted for the detection of antimicrobial resistance in targeting indicator bacteria Staphylococcus aureus at the animal-human-environment interface. A total of 280 samples were collected from dairy farms and their environment. The highest prevalence was noticed in human sources (50%), followed by animal sources (28.50%), dairy equipment (27.50%), and the lowest in farm environments (20.83%), and the overall prevalence noted was 27.85%. The prevalence of species-specific sau gene for S. aureus was 80.76%. Virulence-associated genes viz. sea and seb were detected in 7.93% and 9.52% isolates of S. aureus. The thermostable nuclease nuc gene was found in isolates from animal and human sources with an overall prevalence of 41.26%. Overall antimicrobial resistance pattern of S. aureus isolated from dairy farm and its environment was in the descending order i.e., highest for cefoxitin, erythromycin, amikacin, and clindamycin; moderate resistance was seen in vancomycin and streptomycin, linezolid and tetracycline and the lowest resistance was observed in chloramphenicol, gentamicin, and amoxicillin-clavulanic acid irrespective of the source. In the present study, the prevalence of tetM was 20% (2/10) in farm environments, 1.75% (1/57) dairy animals, and 33.33% (1/3) in dairy equipment with an overall prevalence of 5.19%.