Laboratory detection of MRSA.

The article brings to light an alarmingly high incidence of MRSA (88.9%). Considering the fact that phenotypic screening methods remain the backbone for detection of MRSA in clinical isolates (Babakir-Mina et al., 2012), the authors fail miserably in performing these tests according to CLSI guidelines. This therefore questions the reliability of the data generated making them highly misleading. The authors used 2 McFarland turbidity to perform the Kirby Bauer disc diffusion which is four times the CLSI recommended turbidity of 0.5 McFarland. The study was done between 2008 and 2011 and the authors used 2007 CLSI guidelines for interpretation which are outdated and the results based on it are not relevant. The incubation temperature for oxacillin disc diffusion (DD) is 33°C-35°C and not 37°C. Testing at temperatures above 35°C may not detect MRSA (CLSI, 2008). Oxacillin DD plates should be incubated for 24 hours before reading the zones of inhibition. Oxacillin DD has a sensitivity of only 91% and specificity of only 58.9% while cefoxitin DD has a sensitivity and specificity of 97.8% and 100% respectively (Swenson et al., 2007). CLSI recommends the use of the cefoxitin DD method for detection of MRSA.