Author(s): Bhutia KO, Singh TS, Biswas S, Adhikari L
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Abstract BACKGROUND: Phenotypic methods for the detection of methicillin resistance are inadequate, due to presence of hetero-resistant population and dependence of environmental factors that may affect the phenotypic expression of resistance. AIMS: Present study was conducted, to evaluate the efficacy of phenotypic methods for the identification of species and mec-A mediated resistance in S. aureus with polymerase chain reaction (PCR), and to assess the prevalence of the Panton-Valentine leukocidin (pvl) toxin in methicillin resistant S. aureus (MRSA) and overall S.aureus population. MATERIALS AND METHODS: A total of 200 clinical isolates of Staphylococci were subjected to phenotypic and genotypic methods for the species identification and detection of MRSA. RESULTS: The specificity and sensitivity of conventional methods in the detection of S.aureus, was found to be 100 and 97.59\% respectively. However, the performance of phenotypic methods in the detection of MRSA were: Oxacillin disc diffusion (DD)-sensitivity 70.58\%, specificity 75.75\%; cefoxitin DD-sensitivity 86.27\%, specificity 83.33\%; and oxacillin agar dilution-sensitivity 92.15\%, specificity 90.90\%. PVL gene was detected in all mec-A positive isolates irrespective of their types. CONCLUSION: Phenotypic methods still preferred for the species identification, but for the reliable detection of MRSA an algorithm should include a combination of tests and apply a genotypic method for confirmation of resistance isolates showing discrepant results. Considering the high prevalence of PVL-MRSA, we recommend PCR as assay, as it has an advantage of simultaneous detection of mec-A and pvl genes by multiplex PCR.
This article was published in Int J Appl Basic Med Res
and referenced in Journal of Medical Microbiology & Diagnosis