الفهرس 
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Abstract
The present study aims to investigate the relationship between different SCCmec types and some virulence factors showed by MRSA isolates collected from various clinical sources. Furthermore, this work involves molecular studies for typing of agr system and coa gene by using multiplex polymerase chain reaction (M-PCR) and restriction fragments length polymorphism (RFLP-PCR) techniques, respectively and their correlations to different SCCmec types. Moreover, PCR was used for detection of psm-mec and mecI genes and their relation to SCCmec types. A total of 85 MRSA isolates were identified by using cefoxitin and oxacillin disc diffusion method. MRSA isolates and 6 standard strains were phenotypically investigated for possessing some virulence factors (biofilm, lipase, protease, staphylokinase (SAK), lecithinase, hemolysin and hemagglutination), in addition to PCR technique for detection of toxin encoding genes (hla, hlb, hlg, hld, tsst-1, psm-mec and mecI). Two M-PCRs was used for detection of SCCmec typeshowed that majority of isolates (n=48) and WIS strain were of type V followed by type III that was carried by 17 isolates and 85/2082 strain, 5 isolates of type IX, 3 isolates and N315 strain of type II, 2 isolates and NCTC10442 strain of type I, 2 isolates and CA05 strain of type IV, 2 isolates and HDE288 strain of type VI, 1 isolate of type VIII and 5 isolates could not be classified. There was a significant association between biofilm, SAK and tsst-1 with respect to type V SCCmec. Statistic analysis expressed a highly significant association between type II and III SCCmec and both genes (P value < 0.0001). A typing of MRSA isolates was performed depending on coa patterns by RFLP-PCR with AluI enzyme. Different 30 patterns (C1-C30) were observed among the tested isolates. Finally, M-PCR was performed for agr typing. It was obvious that 52.9%, 31.7%, 5.88% and 9.41% of isolates possessed agr I, agr III, agr II and mixed agr (I+III), respectively. The correlation between SCCmec and agr types was analyzed by dendogram at > 80% similarity showing 25 clusters.