Prevalence, risk factors and multidrug resistance profile of Staphylococcus aureus isolated from bovine mastitis in selected dairy farms in and around Asella town, Arsi Zone, South Eastern Ethiopia

A cross-sectional study was carried out from November 2012 - May 2013 to estimate the prevalence of multi drug resistance Staphylococcus aureus from bovine mastitis and to assess its associated risk factors in selected dairy farms in and around Asella town, Arsi Zone, Ethiopia. A total of 384 fresh raw milk samples from dairy cows were examined for mastitis. Milk samples collected from 251 mastitic lactating cows were subjected to bacteriological examinations for isolation and identification of S. aureus. S. aureus isolates were identified from 44.62% (112/251) mastitic milk samples. Higher prevalence rates of S. aureus isolates were recorded in subclinical mastitis (45.78%, 103/225) compared to clinical cases (34.62%, 9/26), however, no statistically significant difference (p > 0.05) in prevalence of S. aureus between subclinical mastitis and clinical cases. Multivariate logistic regression analysis of the effect of different risk factors on the prevalence of S. aureus revealed that; cross breed (OR = 2.501, 95%CI: 1.173 - 5.334), late stage of lactation (OR = 4.260, 95%CI: 1.9309.402), previous mastitis record (OR = 2.553, 95%CI: 1.3324.894), large sized herd (OR = 15.824, 95%CI: 6.36839.320) and poor udder hygiene (OR = 2.040, 95%CI: 1.184,3.514) were more likely to be infected with antimicrobial resistance S. aureus. All the isolates of S. aureus were subjected to antimicrobial susceptibility testing. The highest rate of susceptibility was to chloramphenicol (97.5%) followed by gentamycin (95.3%), vancomycin (92.7%), and clindamycin (90.9%). Whereas, the highest rate of resistance among the isolates was against penicillin G (87.3%) followed by tetracycline (82.2%), trimethoprim-sulfamethoxazole (69.1%), oxacillin (56.4%), ampicillin (55.1%) and cefoxitin (58.1%). The results of the present study reveal that 65.18% of the isolates were found to be multiple antibiotic resistance phenotypes. Regular antimicrobial sensitivity testing and best practices for achieving hygienic milking should be established.