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ORIGINAL ARTICLE
Year : 2012  |  Volume : 2  |  Issue : 2  |  Page : 84-91

Evaluation of phenotypic with genotypic methods for species identification and detection of methicillin resistant in Staphylococcus aureus


1 Department of Microbiology, Sikkim Manipal Institute of Medical Sciences, 5th Mile, Tadong, East Sikkim, India
2 Molecular Biology Laboratory, Genetix Biotech Asia (P) Ltd, 71/1, First Floor, Shivaji Marg, New Delhi, India

Correspondence Address:
Kunsang O Bhutia
Department of Microbiology, Sikkim Manipal Institute of Medical Sciences, 5th mile, Tadong, East Sikkim
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2229-516X.106348

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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.


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