Mastitis, a major concern in dairy production, significantly affects dairy cows and milk quality. Staphylococcus aureus represents one of the predominant pathogens implicated in bovine mastitis. This study aimed to isolate, identify, and characterize S. aureus from mastitis-positive cows in Central Ethiopia. A cross-sectional study on the isolation, identification, and characterization of S. aureus was conducted from October 2022 to August 2023 in the Hadiya and Kembata zones. Mastitis was diagnosed in lactating cows based on clinical examinations and the California mastitis test (CMT). All mastitis-positive cows were aseptically sampled (milk) for bacterial culture. Isolates were identified through colony characterization, Gram staining, slide catalase, oxidase, and coagulase tests, with species confirmation by MALDI-TOF biotyping. Antimicrobial susceptibility was assessed using the disk diffusion method, and resistance genes were detected by PCR. Out of 376 randomly screened lactating cows, mastitis was identified in 213 (56.6%; 95% CI = 0.52-0.62). Among them, 69 (32.4%) were positive for S. aureus. Significant associations were found between S. aureus mastitis and factors such as the age, tick infestation, and lesions on the skin of the udder and/or teat. All tested S. aureus isolates exhibited resistance to at least two of the nine antimicrobials tested, with 70% being multidrug resistant. The highest resistance rates were observed for penicillin G (100%) and amoxicillin (90%), whereas no resistance was found for cephalothin. All tested isolates possessed the nuc gene, and 90% had blaZ genes; however, mecA genes were not found, including those resistant to cefoxitin. These findings should be interpreted with caution, as antimicrobial susceptibility testing and molecular genotyping were carried out on 10 randomly chosen S. aureus isolates, which may not reflect all isolates. These findings highlight the prevalence of S. aureus-associated bovine mastitis and the occurrence of antimicrobial resistance in Central Ethiopia. The absence of mecA, despite phenotypic resistance, suggests alternative resistance mechanisms. These results underscore the urgent need for antimicrobial stewardship and effective mastitis control strategies to safeguard dairy production and animal health in the region.
Fikru et al. (Mon,) studied this question.