الفهرس 
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Abstract
Among common listed etiological agents causing contagious bovine mastitis, Staphylococcus aureus is topping the list. In addition, they are known to precipitately acquire resistance to accessible antimicrobial agents which in turn upsurge its public health risk and associated consequences. This study investigated S. aureus existence in raw milk samples gathered from 103 cows in dairy farms in Egypt, and disclosed its antimicrobial resistance profile, and related virulence/resistance-encoding genes. Conventional laboratory tests as well as the vitek2 compact system were used to determine and screen the isolates. S. aureus was isolated from (188) mastitis and (224) sub-clinically mastitis milk samples with an incidence of 50% (n=94) and 17.5% (n=39) respectively. Out of 133 positive S. aureus isolates, 69 were randomly selected and subjected to antimicrobial susceptibility testing using a vitek2 compact system whereas they were challenged with a set of 15 antibacterial agents commonly used in the medical and veterinary fields. In addition, 39 isolates were selected randomly and screened for sea, seb, sec, sed, and see enterotoxin-encoding genes by polymerase chain reaction (PCR). The tested isolates exhibited high resistance to Streptomycin, Penicillin-G, and Oxytetracycline while presented high sensitivity to Gentamycin, Amoxycillin +Clavulinic acid and fluoroquinolone antimicrobials (Enrofloxacin and Ciprofloxacin). According to the antimicrobial sensitivity test results, 8 isolates were selected and experienced further molecular typing techniques (PCR and hybridization) for detection of S. aureus virulence genes namely spa, hlg, coa, tst, nuc, clfA, as well as resistance genes blaZ and mecA. Spa gene was the most dominant virulence gene identified in the isolates (n=5), followed by coa and hlg (n=4), nuc and clfA (n=3) and the least detected gene was tst (n=2). The blaZ gene, that is considered the commonest beta-lactam resistance mechanism for S. aureus, was observed in all isolates (n=8/8), while methicillin resistance mediated by mecA gene was noticed in 75% of the screened isolates (n=6/8). None of the isolates possessed sea, sec or sed, while seb and see detected in 13% and 56.5% of the isolates. These results have shown that milk could be a source for transmission of antibiotic resistant S. aureus to humans, hence it is representing an escalating potential public health risk and might adversely affect the treatment options offered to human infected with such strains.