الفهرس 
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Abstract
Staphylococcus aureus has been known to be a major pathogen causing a wide spectrum of clinical manifestations, such as wound infections, pneumonia, septicemia, and endocarditis, with beta-lactam antibiotics being the drugs of choice for therapy. Since the introduction of methicillin into clinical use in 1961, the occurrence of methicillin-resistant S. aureus (MRSA) has steadily increased and nosocomial infections caused by such isolates have become a serious problem worldwide. The differentiation of MRSA strains from other strains of & aureus has important implications for the treatment and management of patients with S. aureus infections. In the clinical laboratory, S. aureus is identified, by growth characteristics and by the subsequent detection of catalase and coagulase activities. Conventional susceptibility testing of S. aureus reliably detects resistance to methicillin or oxacillin if agar dilution tests, disc diffusion tests, or agar screening methods are used according to the standards of the National Committee of Clinical Laboratoy Standards (NCCLS). The aim of this study was the isolation and identification of staphylococci among clinical specimen and detection of methicillin resistance among them both phenotypically and genotypically using conventional laboratory methods and PCR. (3-lactamase production as well as expression of resistance to methicillin were also done. A total of 64 Staphylococci were isolated from patients admitted to the hospital or attending the Microbiology Department of Medical Research Institute over a period of 3 months (September to November 2005). All samples were inoculated on blood agar plates, mannitol salt agar, and DNase agar. Staphylococcal isolates were identified by their colonial and microscopical appearance. Biochemical identification included Catalase test, oxidase test, coagulase Test and Novobiocin susceptibility. Genotypic identification of staphylococci was carried out by detecting nuc gene encoding the thermonuclease enzyme andfemA involved in peptidoglycan biosynthesis. Susceptibility of Staphylococci was determined by, Disc diffusion method including methicillin, oxacillin and cefoxitin discs, MIC testing for oxacillin, Oxacillin agar screening method and p- Lactamase production. Plasmid profile of the Staphylococcal strains was done using QIAGEN® plasmid Mini kit. Plasmid purification protocols are based on a modified alkaline lysis procedure, followed by binding of plasmid DNA to QIAGEN Anion-Exchange Resin under appropriate low-salt and pH conditions. RNA, proteins, dyes, and low-molecular-weight impurities are removed by a medium-salt wash. Plasmid .DNA is eluted in a high-salt buffer and then concentrated and desalted by isopropanol precipitation..