Phenotypic methods of greater accuracy to detect the mecA gene product for the recognition of MRSA in resource constraint settings

Abstract

Objective To evaluate the detection of methicillin resistant Staphylococcus aureus (MRSA) and analyze the performance of Mastalex MRSA (Mast, UK). Methods Two hundred and ten Staphylococcus aureus (S. aureus) strains were isolated from different clinical samples and were tested for methicillin resistance by Oxacillin (1 μg) and Cefoxitin (30 μg) disc diffusion, oxacillin agar screen, and minimum inhibitory concentration of oxacillin and cefoxitin. S. aureus isolates were grown on the blood agar and mannitol salt agar with (2 mg/L) and without oxacillin for the analysis of Mastalex MRSA. Results Out of 210 S. aureus strains tested, 103 strains were detected as methicillin resistant by Cefoxitin disk diffusion, Cefoxitin minimal inhibitory concentration (MIC) and Mastalex MRSA test. Whereas oxacillin disc diffusion and oxacillin agar screen detected 91 and 97 MRSA respectively. The Cefoxitin MIC test performance was equivalent to Cefoxitin disc diffusion. 103 (100%) strains grown on blood agar without and with oxacillin, and 76 (74%) and 93 (91%) strains grown on mannitol salt agar without and with oxacillin shown positive agglutination with Mastalex MRSA test respectively. Conclusions The cefoxitin disk diffusion/Mastalex MRSA is very suitable for detection of MRSA and the tests can be an alternative to PCR for detection of MRSA in resource constraint settings. Mastalex test would be particularly useful when confirmation of resistance is urgently required.