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Int J Appl Basic Med Res. 2012 Jul;2(2):84-91. doi: 10.4103/2229-516X.106348.

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

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1
Department of Microbiology, Sikkim Manipal Institute of Medical Sciences, 5 Mile, Tadong, East Sikkim, India.

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.

KEYWORDS:

fem-A; methicillin-resistant Staphylococcus aureus; phenotypic methods; polymerase chain reaction; pvl

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