ISOLATION, IDENTIFICATION, AND ANTIBIOGRAM OF MASTITIS PATHOGENS FROM MILK SAMPLES OF DAIRY BOVINE IN KATHMANDU VALLEY, NEPAL

ABSTRACT

Background and Aim: Bovine mastitis remains one of the most economically significant infectious diseases of dairy production worldwide and is increasingly associated with antimicrobial resistance (AMR). Monitoring pathogen distribution and cumulative resistance patterns (antibiogram) is essential for disease management and rational antibiotic use. This study aimed to identify mastitis pathogens and develop an antibiogram from isolates recovered from bovine milk samples in the Kathmandu Valley, Nepal.

Materials and Methods: A total of 422 bovine milk samples suspected of mastitis were screened using the California Mastitis Test (CMT) and processed for bacterial culture and identification. Antimicrobial susceptibility testing used the Kirby–Bauer disc diffusion method per standard guidelines, and cumulative data were compiled into an antibiogram. Associations between microbial growth and risk factors (age, parity, species, breed) were analyzed using appropriate statistical tests.

Results: Of 422 samples, 324 (76.8%) yielded microbial growth, comprising 320 bacterial and 4 fungal (Candida spp.) isolates. Staphylococcus spp. (36.7%) predominated, followed by Klebsiella spp. (27.5%), Escherichia coli (8.6%), Pseudomonas spp. (8.6%), and Streptococcus spp. (7.4%), with Enterobacteriaceae (38.8%) and Staphylococcaceae (37.2%) the leading families. Microbial growth was significantly associated with age (p = 0.016) and parity (p < 0.001). The cumulative antibiogram indicated high susceptibility to trimethoprim–sulfamethoxazole, marked ampicillin resistance among Enterobacteriaceae, and emerging β-lactam resistance in Staphylococcus spp. Multidrug resistance was observed in major isolates, including Staphylococcus spp. (17.6%), Escherichia coli (20.7%), and Klebsiella spp. (15.7%).

Conclusion: Bovine mastitis in the Kathmandu Valley was largely bacterial in origin, dominated by Staphylococcus spp. and Enterobacteriaceae, with age and parity as significant risk factors. Beyond herd-level treatment failure, the spread of resistant pathogens through milk threatens animal clinical management and dairy supply-chain safety, a public health concern. The high prevalence of ampicillin resistance, emerging β-lactam resistance, and multidrug resistance among key isolates highlights the urgency of antibiogram-guided antimicrobial stewardship in dairy herds.