One hundred and nineteen clinical samples were isolated from patients admitted in different hospitals in El-Sharkia Governorate. Sixty six isolates were confirmed to be S. aureus. Susceptibility to different antimicrobial agents and Minimum inhibitory concentration tests showed that all the isolates were resistant to 𝛽-lactam antibiotics, 77.2% (n= 51) isolates
were methicillin resistant S. aureus MRSA, while almost all the isolates were sensitive to vancomycin and tigecycline. Polymerase chain reaction (PCR) of mecA, encoding methicillin resistance, and blaZ, β-lactamase biosynthetic gene, revealed the coexistence of both genes in 56.8% (n= 29/51) of the isolates. Meanwhile, 11.7% (n= 6/51) of MRSA isolates phenotypically resistant to oxacillin were found to be mecA-. This data support the fact that the expression of bla genes enhanced the phenotypic expression of oxacillin resistance as a result of β-lactamase hyperproduction. On the other hand, 33% of MRSA (n=17/51) were blaZ– suggesting a mutation event in blaZ or the existence of an alternative mechanisms for 𝛽-lactam resistance that may compete with mecA gene.