الفهرس 
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Abstract
Methicillin resistant Staphylococcus aureus is a highly problematic public health pathogen responsible for a variety of infections. The application of vancomycin as the first-line treatment of MRSA infections led to an upsurge of vancomycin-resistant S. aureus isolates throughout the world. Linezolid is a synthetic antibiotic that was approved against vancomycin resistant strains of S. aureus. It was believed that linezolid resistance would be uncommon, however, several reports in the last decade reported higher incidence of LRSA isolates around the world. The goal of this study is to screen prevalence of MRSA, VRSA and LRSA isolates from different hospitals in Egypt. Additionally, the resistance pattern, some resistance and virulence genes of these isolates was determined. A total of 127 new S. aureus isolates and 96 old isolates were used, MRSA isolates were identified and antimicrobial sensitivity pattern for nine antimicrobial agents from different classes was assessed. PCR identification of vancomycin resistance encoding genes and linezolid resistance genes were performed. Moreover, the prevalence of eight different virulence genes and agr typing of isolates were determined. All isolates were identified phenotypically as MRSA. However, mecA gene was detected only in 95% and 98% of new and old isolates, respectively. The highest and lowest percentage of resistance was recorded for clindamycin (83%) and trimethoprim (12%) in new isolates and nitrofurantoin (5%) in old isolates, respectively. Vancomycin resistance level was 24% and 59% of new and old isolates, while vanA gene was detected only in 17% and 32% and vanB gene was detected in 10% and 11% of new and old VRSA isolates, respectively. optrA gene was detected in 4.17% and 5.8% of new and old LRSA isolates, respectively The highest prevalence of virulence genes was found for icaA, followed by hld, hlb, icaD, hlg, hla, tsst and cna, respectively in the tested isolates. agr type I was the most prevalent among all isolates. Conclusion: This study highlights the alarming problem of the increasing incidence of MRSA, VRSA and LRSA infections in Egypt. Therefore, there is an urgent need to rationalize vancomycin and linezolid consumption and to continuously monitor the prevalence of these strains.