Prevalence of mecA: Genotyping screening of community acquired-MRSA isolates in Karachi, Pakistan.

Among resistant nosocomial and community pathogens, MRSA has become the most serious pathogen, causing life threatening infections worldwide. In S.aureus, quick and exact recognition of methicillin (cefoxitin) resistance has become essential. The benchmark for MRSA identification among S.aureus is the detection of the mecA gene that causes the expression of protein (PBP2a) culpable for classic β-lactam resistance. However, the utter reliance on amplification of mecA gene as a hallmark in confirmation of methicillin (cefoxitin) resistant S. aureus is the matter of distrust by some investigators. The current investigation designed to analyse the prevalence of mecA gene among phenotypically positive MRSA isolates using molecular method and to correlate its prevalence to conventional techniques. Furthermore, antimicrobial sensitivity of mecA positive staphylococci was determined by Kirby Baeuer method. For this purpose, 201 clinical staphylococcal specimens were recovered from various diagnostic laboratories in Karachi City, Pakistan. Phenotypic existence of methicillin resistance in S. aureus was observed to be 51.7%. In contrast, when organisms were subjected for amplification of mecA gene by PCR, mecA positive isolates were 36/104 (35%) MRSA isolates. Current work raise question towards the usefulness of molecular identification of mecA gene in confirmation of methicillin resistance without correlating with conventional methods. Therefore, it is essential to consider the other possible resistance mechanisms for β-lactams that may interact with mecA gene in the development of methicillin resistance mechanism in Staphylococcus.