Objectives: To evaluate and determine the most cost effective, rapid and specific method for detection of methicillin resistance in clinical isolates of S aureus in a setting with limited personnel and resources.
Methods: Standard laboratory methods were used to identify S aureus isolates. The conventional Methicillin Resistance Staphylococcus aureus (MRSA) detection methods used included, 1 μg oxacillin disk diffusion, oxacillin salt agar screen (CLSI), penicillin binding protein (PBP 2 ) latex agglutination test and E-tests oxacillin. Results of conventional tests were compared with a polymerase chain reaction (PCR) method for detecting MRSA isolates. Polymerase chain reaction detection of the mecA gene in S aureus was used as the “gold standard” for MRSA identification.
Results: All methods had 100% sensitivity except for oxacillin disk diffusion and oxacillin-salt agar screening with 98% and 99%, respectively. Specificity was also 100% for all methods except for oxacillin-disk diffusion (99%). Turn around time (TAT) for detection of MRSA was calculated to be within six hours for PCR. The fastest TAT of 1.25 hours was obtained for PBP 2 latex agglutination.
Total cost for labour and materials to perform each method was highest for E-test, US$13.76/isolate. The cost for PCR when compared to that of latex agglutination was not statistically significant (US$3.74 vs US5.91, p = 0.4).
Conclusions: All methods presented high sensitivity and specificity, but the latex agglutination test had the advantage of giving a reliable, rapid and most cost effective result that compares well to PCR in this environment.