Comparison of phenotypic methods with mecA gene based polymerase chain reaction for Methicillin-resistant Staphylococcus aureus detection

Abstract

Objective: To determine methicillin resistance in staphylococcus aureus by different phenotypic methods, and toevaluate their accuracy with mecA gene polymerase chain reaction for methicillin-resistant staphylococcus aureusdetection.

Methods: The descriptive cross-sectional study was conducted from January to December 2015 at the Post-Graduate Medical Institute, Lahore, Pakistan, and comprised consecutive, non-repetitive clinical isolates ofmethicillin-resistant staphylococcus aureus that were screened with oxacillin disk 1ug and cefoxitin disk 30ug byKirby-Bauer method using Clinical and Laboratory Standards Institute guideline. The isolates were cultured onoxacillin screen and mannitol salt agar, and subjected to latex agglutination for penicillin-binding protein 2aandpolymerase chain reaction for mecA gene. Data was analysed using SPSS 20.

Results: All the 105 isolates were resistant on oxacillin and cefoxitin disk diffusion test, but 95(90.47%) were positivefor mecA gene by latex agglutination and polymerase chain reaction. The sensitivity of oxacillin salt agar, mannitolsalt agar and latex agglutination was 94.31%, 96.73% and 98.95%, respectively. Keeping polymerase chain reactionas the gold standard, the specificity and diagnostic accuracy of latex agglutination were 77.77% and 97.14%respectively, which was the highest among all the phenotypic methods.

Conclusion: Latex agglutination method can be proposed as a swiftly reliable diagnostic technique for thedetection of mecA gene in methicillin-resistant staphylococcus aureus isolates in resource-constrained settingswhere molecular methods are limited.

Keywords: Methicillin resistant staphylococcus aureus, Oxacillin, Cefoxitin, Latex agglutination, PCR.