LAUSR

Abstract Background Among bacterial pathogens, Staphylococcus aureus which lives in the mammary gland is the leading cause of bovine mastitis worldwide, which causes enormous economic losses to the dairy industry. Objectives and methods The study was carried out cross‐sectionally to determine the occurrence of methicillin‐resistant S. aureus (MRSA) and the risk factors for mastitis infection in dairy cows in and around Adama from October 2014 to June 2015. This particular study included 384 animals. Milk samples were collected and screened with California mastitis test. Then bacteria were cultured and identified using biochemical tests and disc diffusion test was used to determine the antimicrobial sensitivity for MRSA. Results The prevalence of mastitis was 121 (31.5%). Among them, 37 cases (30.6%) were clinical mastitis and 84 cases (69.4%) were subclinical mastitis. Among these positive cases, 37 cases (30.6%) of S. aureus were isolated. The prevalence of mastitis was significantly related to the breed, age, floor type and sanitation status of the milking (p <0.05). The Kirby–Bauer disc diffusion method was performed on Mueller Hinton agar medium according to NCCLS guidelines to test antibiotic sensitivity. The 32.4% of S. aureus isolates were resistant to oxacillin. Isolates of MRSA are more resistant to amoxicillin (75%), oxytetracycline (66.7%) and sulfa (50%). However, they were sensitive to kanamycin (75%), streptomycin (58.3%) and nalidixic acid (50%). Insufficient dosage, short treatment time and chronic infection in dairy cows in the herd are the main reasons for the large number of resistant strains. Conclusion and recommendation Generally, mastitis was prevalent in the area, and it was resistant to commonly used antibiotics. Therefore, hygienic, prevention and alternative treatment methods should be implemented.