Staphylococcus aureus isolates from cow’s milk in dairy farms at Shinshicho town, Kembata Tembaro Zone, Southern Ethiopia: Prevalence, risk factors, and antimicrobial susceptibility profile

Bovine mastitis is an economically important and highly prevalent infectious disease in dairy herds worldwide. Staphylococcus aureus is a  common microorganism causing infectious mastitis. A cross-sectional study was conducted between December 2018 and September  2019 in Shinshicho town, Kembata Tembaro Zone, Southern Ethiopia, to estimate the prevalence, and assess associated risk factors and  antimicrobial susceptibility profile of S. aureus isolates from cow’s milk in dairy farms at Shinshicho town. Lactating dairy cows were  screened for mastitis based on clinical examinations and the California mastitis test (CMT) followed by laboratory identification of S.  aureus. All the S. aureus isolates were subjected to antimicrobial susceptibility tests using a disk diffusion test. Multivariable logistic  regression analysis of the effect of different risk factors on the prevalence of mastitis was performed. From a total of 384 lactating cows  examined and tested, 41.7 % ( n=160) were found positive for mastitis. Out of the occurrences of mastitis, 5% (n=19) and 36.7% (n=141) were clinical and subclinical respectively. Staphylococcus aureus was isolated from 36.84% (n=7) and 39.01% (n=55) of the clinical and  subclinical mastitis respectively with a total isolation frequency of 38.75 % (n=62). According to the results of this study, greater herd sizes  (OR=2.91, 95% CI: 1.62-5.21), higher parity cows (OR=3.91, 95% CI: 1.73-8.82), late lactation stage (OR=3.36, 95% CI: 1.27-8.91), and  muddy floor (OR=2.37, 95% CL: 1.31-4.27) are risk variables linked to the occurrence of S. aureus mastitis. In addition, S. aureus has total  resistance to ampicillin, amoxicillin, penicillin-G, and Polymyxin. Similarly, 53.2% of the isolates proved resistant to three or more of the  antibiotics used. Therefore, regular antimicrobial susceptibility testing should be performed to select potent modified antibiotics, and the  effects and dynamics of genetic determinants of antibiotics should also be studied using molecular methods.