Serological identification of group A streptococci from throat scrapings before culture.

The use of a microtechnique (modified nitrous acid extraction) to test samples from 150 school children and from patients with acute follicular tonsillitis has indicated that group A streptococci in the throat can be identified from tonsillar scrapings in 30 min. The results are comparable to the grouping results obtained by standard throat culture techniques and the Lancefield procedure for grouping. No cross-reaction with other bacteria or cellular material occurs. Study has also shown that the nitrous acid extraction yields three- to fourfold more polysaccharides than the Lancefield hot-HCl of Fuller formamide techniques. The use of the microtechnique leads to another 20-fold concentration of the antigen. Immune salting-out effect could be obtained with 1.00 M sodium acetate. Such molarity is too low to cause nonspecific slating out. It leads to a strong ampliciation of the precipitin reaction.