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

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

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 of methicillin-resistant staphylococcus aureus that were screened with oxacillin disk 1μg and cefoxitin disk 30μg by Kirby-Bauer method using Clinical and Laboratory Standards Institute guideline. The isolates were cultured on oxacillin screen and mannitol salt agar, and subjected to latex agglutination for penicillin-binding protein 2aand polymerase 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 positive for mecA gene by latex agglutination and polymerase chain reaction. The sensitivity of oxacillin salt agar, mannitol salt agar and latex agglutination was 94.31%, 96.73% and 98.95%, respectively. Keeping polymerase chain reaction as 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.

Conclusions: Latex agglutination method can be proposed as a swiftly reliable diagnostic technique for the detection of mecA gene in methicillin-resistant staphylococcus aureus isolates in resource-constrained settings where molecular methods are limited.