ABSTRACT
Methicillin resistant Staphylococcus aureus [MRSA] is an important pathogen causing severe nosocomial infections whose prevalence has been increasing. The effectiveness of infection control measures is enhanced by early detection of resistant isolates and this is dependent on the time taken to isolate and identify MRSA In specimens taken from infected patients and in screening specimens taken to identify patients colonized with MRSA. So we aimed in this study to evaluate the abilities of phenotypic methods [Disk diffusion. E-test and Latex agglutination test] and genotypic method [real time PCR] for rapid detection of methicillin resistance in S. aureus. It was done on 220 patients [155 males and 65 females] at Benha University Hospital during the period from March to September 2005 to isolate any growth of S. aureus. Two hundred and twenty clinical samples were collected: they were 140 pus samples. 48 urine samples and 32 blood samples. Pus and urine samples and positive blood cultures were cultured to isolate any growth of S. aureus then the isolated colonies were examined for identification of MRSA isolates by disk diffusion method [Ox 1 micro g. Ox 5 micro g and Fox 30 micro g]. E-test. PBP2a latex agglutination test and detection of mecA gene by real time PCR. Two hundred isolates were detected in 220 clinical samples The frequency of S. aureus isolates was 28% [56 out of 200 isolates] they were mainly from wound pus [36 out of 56] The mec A PCR assay allowed us to classify 22[39.3%] of the isolates as S. aureus mec A-positive and they were mainly from pus [12 out of 22] and blood [6 out of 22]. and 34 [60.7%] as S aureus mecA negative. When phenotypic and genotypic identification was compared with PCR results it was found that by oxacillin 1 micro g disk, the sensitivity was 90.9% and the specificity was 94.1% by oxacillin 5 micro g disk, the sensitivity was 90.1% and the specificity was 76.5%, while cefoxittin 30 micro g disk yield 100% sensitivity and 94.1% specificity. Oxacillin E-test strips had the same sensitivity and specificity of oxacillin lmicrog disk. Latex agglutination test and real time PCR had the best sensitivity[100%] and specificity [100%] and they are able rapidly and reliably to detect MRSA isolates. the new molecular assay [real time PCR] was found to be rapid and robust because it is a largely automated assay. less hands on work is needed, consumes shorter time than conventional PCR and it can be used for direct detection of MRSA from non sterile clinical specimen, however, it is not yet available in the majority of routine diagnostic laboratories because of their elevated technical requirements. In absence of real time PCR. latex agglutination test is the best method for MRSA detection from isolated colonies