Abstract
Staphylococcus aureus is one of the most important pathogens of humans and animals, asymptomatically colonizes the anterior nares of humans and animals and it is considered one of the most significant etiological agents of intramammary infection in dairy ruminants, causing both clinical and subclinical mastitis, causing wound infection and dermatitis.
A total number of 164 samples (mastitic milk, nasal swabs, wound swabs, abscesses′ contents) were collected from ruminant animals (cattle, sheep and goat) either individually or from farms in Alexandria governorate and subjected to bacteriological examination.
Seventeen Staphylococcus aureus isolates were identified morphologically, biochemically. Antibiogram profile of the isolates were carried out against 11 antimicrobials. 16/17 (94%) of isolates showed resistance to at least one antimicrobial, 11/17(64.75) of the isolates showed resistance to three or more of antimicrobials (multi-drug resistance), the highest sensitivity was observed for vancomycin and amoxicillin/clavulanic acid 17/17 (100%) while the highest resistance was observed for penicillin 14/17 (82%), and gentamicin 9/17(53%). Eight out of seventeen isolates (47%) showed resistance to oxacillin/cefoxitin (methicillin resistant S. aureus) all of them were multi drug resistant (MDR).
Ten of MDR S. aureus isolates were molecularly screened for integron. Class 1 integron cassette were detected in 1/10 of tested isolates which exposed to further sequence analysis revealing dfrA15 gene cassette which encodes trimethoprim resistance that firstly reported in S. aureus isolates. The GenBank accession number of the dfrA15gene sequences determined in this study is MW036489.

Key words: Staphylococcus aureus, Ruminants, Multi drug resistance, Integron, gene cassette.