Simplified extraction procedure for serological grouping of beta-hemolytic streptococci.

An adaptation of the nitrous acid extraction of streptococci proved to be a reliable and practical method for the preparation of extracts for routine serological group identification. The extracts of all groups tested gave strong capillary precipitin reactions as well as reactions of double diffusion in gel. For routine grouping, extracts were prepared from the first one-half-plate subculture of the initial throat culture. The technique is simple and reliable, and it requires a minimum of technical skill, reagents, and equipment. Its use would facilitate epidemiological surveillance of group A streptococci and rapid diagnosis of streptococcal infections at a low cost.