Isolation, Identification, and Antibiogram Characteristics of Staphylococcus aureus From Dairy Cows Kept Under Extensive Management System, in the Uba DebreTsehay District of Southern Ethiopia

Abstract

Bovine mastitis is a widespread and important disease of cows that affects the global production and quality of milk in the dairy industry. A cross-sectional study conducted from February to August 2022 in the Uba Debretsehay District aimed to determine the prevalence of bovine mastitis, assess the associated risk factors and the antibiotic susceptibility profiles of Staphylococcus aureus isolates from mastitis-positive cows. A total of 432 cows were screened through clinical examinations and the California mastitis test to determine the occurrence of clinical and sub-clinical mastitis respectively. A milk sample was collected from mastitis-positive cows and standard microbiological procedures were used to identify S. aureus. Antimicrobial susceptibility testing was performed using 10 antimicrobials following the Kirby–Bauer disc diffusion method. The overall prevalence of mastitis was 44.2% (191/432; 95% CI = 0.37–0.51) and 41% (702/1728) at the cow and quarter level respectively. The odds for the occurrence of mastitis significantly decreased without tick infestation and or injury (OR = 0.15; 95% CI = 0.07–0.28), and the previous history of mastitis (OR = 0.28; 95% CI = 0.17–0.47). Cows in mid-stage lactation were 2.13 times more likely to develop mastitis than early-stage lactating cows. Additionally, cows kept with in larger herds were 1.57 times more prone to mastitis than those on small herd size. Out of the 191 mastitis-positive milk samples, S. aureus was isolated in 2.6% (5/191) of these samples using the BioLog microbial identification system. S. aureus isolates showed no susceptibility (0%) to penicillin G or tetracycline, but exhibited 100% susceptibility to amoxicillin-clavulanate, cefoxitin, ciprofloxacin, chloramphenicol, oxacillin, trimethoprim-sulphamethoxazole, and gentamicin. Mastitis is a severe problem for dairy production in the study area, and the resistance of S. aureus to commonly used antibiotics was observed. Therefore, proactive management strategies including adequate sanitation of the dairy environment, regular screening of animals, and rational use of antibiotic agents were recommended to maintain the productivity and well-being of dairy cows in the study areas.