Application of serum opacity factor in subtyping of group A streptococci & identification of new M-types.

Out of 742 isolates of group A streptococci (GAS), 34.0 per cent were positive for production of serum opacity factor (SOF). The T and M typability of these GAS strains was 93.3 and 10.8 per cent respectively. Clustering of the strains under the T patterns 5/12/27, 8/25/Imp. 19 and 3/13/B3264 and low M typability indicated the utility of SOF testing as an additional marker in epidemiological characterisation of GAS. SOF was further found to be useful in identification of new M type and simplified M typing by saving time, labour and sera.