Abstract
Rapid and accurate detection of Methicillin Resistant Staphylococcus aureus (MRSA) is an important role of clinical microbiology laboratories to avoid treatment failure. The detection of MRSA is based on phenotypic assays which require at least 24 h to perform. Detection of the mecA gene or of PBP 2a is the “gold standard”, but not always available. The aim of this study was to evaluate a rapid method for detection of MRSA by using 3 (4, 5 dimethyl thiazole -2-yl) -2, 5 diphenyl tetrazolium bromide (MTT). Total 126 isolates of MRSA were collected from tertiary healthcare center and were confirmed by oxacillin screening agar test as per CLSI guidelines. Amplification of mecA gene was performed by using PCR. MTT assay was carried out for all the isolates in 96 well Microtitre plate and compared with standard methods of CLSI. Out of 126 isolates, 98 were found to be mecA positive. MTT method was found to be 98.98% sensitive and 96.43% specific. The MTT based colorimetric method is rapid and simple test for screening of oxacillin resistance in Staphylococcus aureus. It significantly shortens the time to just 7 h required to obtained a drug susceptibility test and could be useful to screen MRSA.
Highlights
Is based on phenotypic assay such as disk diffusion and broth micro dilution[9]
Total 126 strains of S. aureus were tested by different methods recommended by CLSI along with the MTT based rapid colorimetric method
All oxacillin resistant strains were correctly identified by their higher MIC’s on the basis of resistance criterion given by CLSI guidelines for Antimicrobial Susceptibility testing and Microbial drug resistance
Summary
Is based on phenotypic assay such as disk diffusion and broth micro dilution[9]. Culture requires longer turnaround time of about 18–48 h with low sensitivity and 100% specificity[10]. Whereas detection of mecA gene or PBP2a is the ‘Gold Standard’ offering high sensitivity and rapid results but these methods are not always been possible in many facilities constrains laboratories[11] of developing countries like India. For this reason rapid and reliable antibiotic susceptibility testing method for detection of MRSA is needed[12]. MTT is a yellow tetrazolium salt which is converted into a blue formazan by dehydrogenase of live cell This method is based on the principle that the amount of formazan produced is directly proportional to the number of live cells[13]
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