469DETECTION OF ERYTHROMYCIN RESISTANCE AND SERUM OPACITY FACTOR IN GROUP A STREPTOCOCCI CAUSING PHARYNGITISGroup A Streptococcus (GAS) accounts for the major etiological agent for pharyngitis in our population. Serum opacity factor is a virulence determinant expressed by GAS, which mediate in adhesion of GAS to the mucosal epithelial cells. This study is aimed to detect the prevalence of GAS in causing Pharyngitis in our population and also to study the antibiotic resistance pattern and their ability to produce SOF of the isolates. A total of 430 children with pharyngitis were screened for GAS infection. GAS in 71 cases was confirmed by standard microbiological protocol. Antibiotic susceptibility testing was done by Kirby Bauer’s disc diffusion test. Macrolide resistance was confirmed by minimum inhibitory concentration test. Serum opacity factor (SOF) was detected by tissue culture plate method. Out of total 71 GAS isolates, 38 (53.52%) were positive for SOF production. All the GAS isolated was completely sensitive to Penicillin, Amoxicillin, Cephalothin and cefuroxime but showed 28.1% resistance to Erythromycin, 11.26% to Clindamycin. 12.7% to Ofloxacin and 17% to Chloramphenicol. The present study showed significantly high rate of GAS pharyngitis infection in Chennai and Macrolide resistance is also on the rise which needs to be given attentionshabanarazmin@gmail.comResearch562014GAS,Serum opacity factor,Erythromycin resistanceShabana Praveen,Prema A Department of Microbiology, SRM medical college, Katankulathur, Tamilnadu, India.,Department of Paediatrics, SRM medical college, Katankulathur, Tamilnadu, India