Assessment of Antimicrobial Resistance Patterns of Bacterial Isolates from Mastitic Milk in Dairy Herds in Benue State

Bovine mastitis is the most economically significant disease in dairy cattle globally and in Nigeria, causing reduced milk yield, increased treatment costs, and premature culling. The irrational use of intramammary and systemic antibiotics without culture-guided selection has accelerated the emergence of resistant bacterial strains in Nigerian dairy environments. This study isolated and characterised bacteria from mastitic milk samples collected from dairy cows in Benue State, North Central Nigeria, and evaluated their antimicrobial susceptibility profiles. Quarter milk samples were collected aseptically from 80 cows with clinical or subclinical mastitis identified by the California Mastitis Test at farms in Makurdi and Otukpo. Samples were cultured on blood agar and MacConkey agar, and isolates were identified by standard microbiological techniques. Antimicrobial susceptibility testing was performed by the Kirby-Bauer disk diffusion method. Staphylococcus aureus was the most frequent isolate at 42.3 percent, followed by Streptococcus agalactiae at 24.6 percent and Escherichia coli at 18.9 percent. Multidrug resistance was detected in 56.7 percent of Staphylococcus aureus isolates, with resistance to penicillin, ampicillin, and tetracycline commonly co-occurring. Methicillin-resistant Staphylococcus aureus was confirmed in four isolates by the cefoxitin disk test. These findings underscore the public health significance of mastitis management in Benue State dairy herds and highlight the urgency of implementing culture-guided antibiotic selection, antibiotic stewardship programmes, and surveillance for resistant pathogens in the North Central dairy sector. Keywords: mastitis, antimicrobial resistance, Staphylococcus aureus, dairy cattle, Benue State.