Isolation and identification of methicillin-resistant Staphlococcus aureus from mastitic dairy cows in Bishoftu town, Ethiopia

This study determines prevalence of methicillin-resistant S. aureus from bovine mastitis in dairy cows from October 2012 to June 2013 in Bishoftu town, Ethiopia. In this cross-sectional study, 16 dairy farms were included and 384 lactating cows sampled. Clinical examination and California mastitis test (CMT) were performed to diagnose clinical and subclinical mastitis, respectively. Milk samples were obtained from the quarters that reacted positively to California mastitis test and cultured to isolate S. aureus. Antimicrobial sensitivity test was conducted on the isolates using antibiotics including penicillin G (10 IU), amoxicillin (25 μg), streptomycin (10 μg), erythromycin (15 μg), oxacillin (1 μg), chloroamphenicol (30 μg), vancomycin (30 μg) and ampicillin (10 μg), all from Oxoid and tetracycline (30 μg) and gentamicin (10 μg) with agar diffusion technique. Data were analyzed using Statistical Package for Social Science. Results reveal that of the 384 milk samples collected and subjected to CMT examination, 177(46.09%) were found to be mastitis positive, of which 23(12.99%) and 154(87%) showed clinical and subclinical mastitis, respectively. Of the 177(46.09%) mastitis positive cases, S. aureus was isolated in 110(28.65%) samples. The antibiotic susceptibility test indicated that the highest resistance was observed for penicillin (100%) followed by oxacillin (65.45%), erythromycin (61.82%) and amoxacillin (59.09%). There was a statistically significant difference (P<0.05) between S. aureus prevalence and risk factors (age and lactation stage). This study indicates that there is high existence of methicillin-resistant S. aureus in dairy cows. Therefore, public awareness on transmission, prevention and control of methicillin-resistant S. aureus is suggested.