Prevalent bacterial pathogens in bovine mastitis and their antimicrobial susceptibility pattern in Nigerian breeds of cattle

Bovine mastitis is an economically important disease globally and, most importantly, in the tropics. Inadequate data on mastitis and the increasing prevalence of antimicrobial resistance (AMR) in livestock pathogens pose significant threats to animal health and public safety. This study investigated bacterial pathogens involved in bovine mastitis and their sensitivity to commonly used veterinary antimicrobial drugs. We screened cows that naturally manifested clinical symptoms of mastitis by taking their milk samples and confirmed them with modern rapid diagnostic test strips, and standard microbiological methods were used to isolate prevalent bacterial organisms. Isolates were subjected to antimicrobial susceptibility testing (AST) using the Kirby–Bauer disc diffusion method. Susceptibility was categorized as sensitive (S), intermediate (I), or resistant (R) on the basis of a standardized zone of decreasing diameter. Findings revealed more clinical mastitis in White Fulani (51.22%) and in older (96.77%) cows than in other breeds and younger cows. The organisms isolated were Pseudomonas spp (38.71%), E. coli (25.81%), Klebsiella spp (19.35%), Staphylococcus spp (12.90%), and Streptococcus spp (3.23%). The overall sensitivity across all the isolates was low, ranging from 31.82% (Streptococcus spp.) to 54.55% (Pseudomonas spp. and E. coli). We observed 100% sensitivity of almost all the isolates to the penicillin‒streptomycin combination, suggesting high synergistic efficacy. These findings highlight the high burden of multidrug resistance (MDR) among the tested pathogens, with Streptococcus isolates proving the most difficult to treat. Widespread resistance to oxytetracycline and amoxicillin necessitates urgent antibiotic stewardship to mitigate the spread of AMR in livestock environments.