Comparative Study of Inducible and Constitutive Clindamycin Resistance among Methicillin Resistant Staphylococcus AureusIsolates.

INTRODUCTION : Staphylococcus aureus is the commonly encountered pathogen isolated from clinical specimens. Methicillin Resistant Staphylococcus aureus (MRSA)causes variety of human infections resulting in high rate of mortality and morbidity.Clindamycin, lincosamide antibiotic is a good option for clinicians to treat MRSA infections. AIMS AND OBJECTIVES : The aim of the study was to screen for MRSA by disc diffusion method with cefoxitin and oxacillin discs and to determine the prevalence of inducible clindamycin resistance and constitutive clindamycin resistance in MRSA and compare them. MATERIALS AND METHODS : 200 staphylococcus aureus were isolated from samples like pus, blood, sputum, vaginal swab, urine and body fluids received in microbiology department of Coimbatore Medical College Hospital.They were confirmed by microscopy,culture and biochemical reaction. Then MRSA were detected by disc diffusion test using Cefoxitin (30μg) and Oxacillin(1μg) discs. Clindamycin resistance were detected by performing D-test by placing erythromycin 15μg and clindamycin 2μg discs at 15-20mm interdisc distance. RESULTS : Majority of staphylococcus aureus were isolated from pus samples (87.5%). Staphylococcus aureus was highly sensitive to linezolid (100%) and vancomycin (99%) and 100% resistant to penicillin. Cefoxitin disc detected higher percentage (26%) of MRSA than oxacillin disc (24%). Analysis of clindamycin resistance in 52 (26%) MRSA isolates showed 42.30% of inducible clindamycin resistance, 30.76 % of constitutive clindamycin resistance and 26.92% were sensitive to both erythromycin and clindamycin. CONCLUSION : Detection of MRSA is very important for treating patients and to prevent its spread. MRSA isolates exhibiting inducible clindamycin resistance are seemed to be susceptible to clindamycin in vitro but resistant invivo resulting in treatment failure. So‘D’test is suggested along with routine antibiotic susceptibility testing to detect inducible clindamycin resistance.