Antimicrobial resistance and virulence profiles of MRSA and MRCoNS across the livestock-human-environment nexus in Karnataka.

Staphylococcus species, particularly Methicillin-resistant Staphylococcus aureus (MRSA) and Methicillin-resistant coagulase-negative Staphylococci (MRCoNS), are salient pathogens in both humans and animals. Their potential to attain antimicrobial resistance genes (ARGs) and biofilm formation contributes to persistent infections, treatment failure, and zoonotic transmission. Based on the One Health approach, this study investigated the ubiquity, antimicrobial resistance, and biofilm gene profiles of MRSA and MRCoNS from apparently healthy livestock, animal handlers, and environmental sources in South Karnataka, India. A total of 740 samples were collected through multistage random sampling, comprising healthy livestock (n = 480), animal handlers (n = 130), and the environment (n = 130). Multiplex PCR was used to identify the isolates to the species level, and methicillin resistance was detected phenotypically and by mecA gene amplification. Antimicrobial susceptibility was assessed by Kirby- Bauer disk diffusion. mecA positive MRSA was found in 26 isolates (5.42 %) from livestock, 6 (4.62 %) from animal handlers, and 2 (1.53 %) from the environment, while MRCoNS was found in 24 (5 %), 7 (5.38 %), and 1 (0.76 %) isolates, respectively. Resistance was most frequent to penicillin and cefoxitin in livestock-human-environmental interface, followed by linezolid, while enrofloxacin and chloramphenicol showed the highest susceptibility in the animal-human and environmental interface. These findings emphasize the presence of livestock isolates carrying significantly higher numbers of resistance and biofilm genes compared to handler and environmental isolates, underscoring their role as the main reservoir of AMR at the One-Health interface. Continuous surveillance and a One Health-based approach are essential to mitigate transmission risks between animals, humans, and the environment.