Comparison of Cefoxitin Disc Diffusion Test with Polymerase Chain Reaction(PCR) to Detect mecA Gene for Detection of Methicillin Resistant Staphylococcus aureus

Abstract

Background Methicillin-resistant Staphylococcus aureus is a persistent and ever growing problem for health-care institutions. The hospital-acquired methicillin-resistant Staphylococcus aureus is a threat to appropriate, efficient and beneficial therapy of the patients. Again the worldwide emergence of community-acquired MRSA is a threat to individuals both in the community and in the hospital environment as these strains are more virulent than the hospital-acquired MRSA strains. Furthermore community-acquired MRSA have started to replace hospital-acquired MRSA in health-care settings. Objectives: 1. To compare Cefoxitin disc diffusion test with PCR to detect mecA gene for detection of methicillin-resistant Staphylococcus aureus, 2. To detect prevalence of methicillin- resistant Staphylococcus aureus. Materials and methods: All Staphylococcus aureus isolated from different clinical samples received in Microbiology Department of J.N.M.C Belgaum, from January 2013 to December 2013 were included in this study. The Staphylococcus aureus isolates were reconfirmed by gram staining, by the characteristic growth on blood agar and nutrient agar and by putting up biochemical reactions. Routine antibiotic sensitivity testing to the antibiotics- ampicillin, amoxyclav, ciprofloxacin, clindamycin, gentamycin and erythromycin carried out. Cefoxitin (30 microgram) disc diffusion test done for all the isolates. PCR carried out for 60 of the isolates which were selected by systematic sampling. Results: Out of the 372 isolates, 160 were methicillin-resistant by Cefoxitin disc diffusion test. 60 of the isolates were taken based on systematic sampling. By PCR, of these 60 isolates 48 were mecA positive (methicillin-resistant) and 12 were mecA negative (methicillin-sensitive). Whereas by Cefoxitin disc diffusion, 42 were MRSA and 18 were MSSA. Prevalence of MRSA was 43% on screening by Cefoxitin disc diffusion test. Conclusion: Accurate detection of methicillin-resistant Staphylococcus aureus is essential for proper treatment of patients and also to monitor their response to the various antibiotics. The present study provides an evidence that Cefoxitin disc diffusion test can be used effectively on a routine basis for screening of methicillin-resistant Staphylococcus aureus as it has a specificity of 100%. But the role of PCR is undisputable in detection of mecA gene for MRSA as Cefoxitin disc diffusion test had a sensitivity of 87.5%.