Comparison of Oxacillin and Cefoxitin for the Detection of mecA Gene to Determine Methicillin Resistance in Coagulase Negative Staphylococci (CoNs)

The aim of the study was to compare the effectiveness of Cefoxitin with that of Methicillin/Oxacillin in the determination of mecA gene in Methicillin resistant Coagulase-negative staphylococci (CoNS). We assessed 57 CoNS isolates for mecA gene via PCR, which were subsequently subjected to Methicillin/Oxacillin and Cefoxitin disc diffusion test. These methods are simple, inexpensive and easily available compared to PCR despite less specificity. Out of 41 mecA positive species, 33 (80.5%) were resistant to Methicillin/Oxacillin. Cefoxitin-resistance was seen in all 41 (100%) mecA positive samples. Two (12.5%) mecA negative isolates of S. saprophyticus were Methicillin/Oxacillin resistant, but were Cefoxitin sensitive. Four (9.7%) isolates of S. saprophyticus, three (7.3%) of S. epidermidis species, and one (2.4%) S. haemolyticus that were mecA positive were sensitive to Methicillin/Oxacillin but resistant to Cefoxitin. Cefoxitin resistance provides a more accurate picture of mecA gene positivity as compared to Methicillin and Oxacillin.