Abstract
Staphylococcus aureus is commonly associated with mastitis in dairy herds with potential public health implications. Overall, 303 samples were collected from September 2015 to July 2016 to characterize the phenotypic and genotypic pattern of drug resistance in S. aureus isolated from cases of clinical and sub-clinical bovine mastitis in Central Ethiopia. Milk samples were tested by using California Mastitis Test and positive samples were subjected for bacterial culture, disc diffusion test and polymerase chain reaction (PCR) to detect the presence of antimicrobial resistance. Based on California mastitis test (CMT) result and clinical examination, the prevalence of mastitis was 70.6%. S. aureus was isolated from 36.9% of CMT positive samples. The phenotypic determination of antimicrobial resistance showed that the isolates were most resistant to ampicillin (80%) followed by trimethoprim-sulfamethoxazole (23.3%), tetracycline (15%), streptomycin (10%) and gentamycin (3.3%) and equally to both erythromycin and chloramphenicol (1.6%). Characterization of the antimicrobial resistance gene was done by using PCR. Most of the isolates (56%) contained blaZ gene followed by ermB (33%), ermC (13.3%) and each ermA and msrA appeared only in 2% of the isolates. There was no isolate harboring the methicillin resistance mecA gene. Thirty six percent of the isolates contained more than one antibiotic resistance genes. The highest multidrug resistance (MDR) gene combination was observed by blaZ*ermB (31.25%) genes and the least frequently occurred were blaZ *ermA and msrA*ermB (3.12%) each. This study showed that consumption of raw milk could be considered as a critical source of antibiotic resistant S. aureus. Key words: Bovine mastitis, Staphylococcus aureus, antimicrobial resistance, Ethiopia.
Highlights
Mastitis is one of the most important diseases in dairy significant economic losses to the dairy industry
The prevalence of bovine mastitis was found in 70.6%
This prevalence of mastitis is comparable with previous reports from Ethiopia who reported a prevalence rate of 71.0 and 75.2% in dairy farms located at Holetta and Jimma towns, respectively (Sori et al, 2011; Mekibib et al, 2009)
Summary
Mastitis is one of the most important diseases in dairy significant economic losses to the dairy industry. Staphylococcus aureus causes one of the most common types of chronic and cows throughout the world and is responsible for subclinical mastitis in dairy animals. The inappropriate use of antibiotics for medication and growth enhancers in farm animals contributes for emergence of antibiotic resistant organisms. It is more than two decades since the emergence of antimicrobial resistant in staphylococci(Lowy, 2003). Health the main etiological agents of mastitis in dairy cattle and cows are the second largest reservoir of S. aureus next to human nares and up to 75 million of cows can be infected by this bacterium form the world cattle population (Sakwinska et al, 2011; Somayyeh and Habib, 2014; Raney, 2009). The overall loss due to mastitis ranges from 31 to 749 kg in first lactation to losses between 117 and 860 kg in subsequent lactation (Hultgren and Svensson, 2009; Ostergaard and Grohn, 1999)
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