Incidence of Methicillin Resistant Staphylococcus aureus [MRSA] in Pus Samples and Associated Risk Factors in a Tertiary Care Hospital

Background: Staphylococcus aureus is a human pathogen with a remarkable propensity for development of antibiotic resistance. The aim of our study is to correlate the phenotypic and genotypic methods and to study the associated risk factors for methicillin resistant Staphylococcus aureus [MRSA] in pus samples. Material and Methods: A total of 200 clinical pus samples were collected. Routine antibiotic susceptibility testing was performed including oxacillin disk [5µg]. Oxacillin screen agar plates with 4% NaCl and 4 µg /ml, 6 µg /ml, 8 µg /ml of oxacillin were inoculated and interpreted as per standard guidelines. Cefoxitin disk diffusion test was performed using 30µg disc and zone sizes were measured. PCR for mec A gene was performed. Associated risk factors like sex, diabetic or not, hospital acquired or community acquired and diabetes was also considered. Results: Out of 200 clinical pus samples 80 strains were isolated as Staphylococcus aureus. Among them 28 were found to be MRSA by cefoxitin disc [30-µg] test and 29 by mec A gene. Cefoxitin results with 96.55% and 96.22% sensitivity and specificity respectively. Cefoxitin is less specific and sensitive to PCR, gold standard for detection of MRSA but is more sensitive to oxacillin agar screen [8µg].