Abstract

Mastitis remains one of the most economically significant diseases in dairy cattle, with antimicrobial therapy as the cornerstone of treatment. Indiscriminate use of critically important antimicrobials such as enrofloxacin has accelerated the emergence of antimicrobial resistance (AMR), raising serious concerns for both animal and public health. A total of 80 bovine milk samples from clinical mastitis cases submitted to the Department of Veterinary Epidemiology and Preventive Medicine, Kerala (2020–2024), were bacteriologically examined. Isolates were identified by colony morphology, Gram staining, and biochemical characterisation. Antimicrobial susceptibility testing against enrofloxacin was performed using the Kirby–Bauer disc diffusion method following CLSI (2017) guidelines, and temporal trends in resistance were analysed. Of 80 samples, 65 (81.25%) yielded Grampositive bacteria (Staphylococcus spp., 87.69%; Streptococcus spp., 12.30%) and 15 (18.75%) were Gram-negative (Escherichia coli, 73.33%; Klebsiella spp., 13.33%; Pseudomonas spp., 13.33%). Enrofloxacin demonstrated high efficacy (≥70–100% sensitivity) during 2020– 2021; however, resistance rose steadily from 2022 onwards, with complete resistance (100%) recorded in multiple months of 2023–2024. Sporadic sensitivity recovery was observed in late 2024, though resistance remained predominant. The rapid emergence of enrofloxacin resistance within 2–3 years highlights the misuse and overuse of antimicrobials in dairy herds. Strengthened antimicrobial stewardship, drug rotation, routine susceptibility testing, and farmer education are essential to safeguard antimicrobial effectiveness in both veterinary and public health contexts.

Keywords : Bovine mastitis; antimicrobial resistance; enrofloxacin; dairy cattle; One Health