Growth Media for Typing Group a Streptococci.

It is frequently not possible to type group A streptococei. Only 33% of group A streptococei from Nashville children in a recent study (Quinn and Martin, Am. J. Hyg. 73:193, 1961) were typable, and there have been years when as few as 5% could be typed. This study was designed to test one possible reason for failure to type certain strains of group A streptococci, namely, inadequacy of growth medium. Typable and nontypable strains of group A were studied, the former to compare the quantity of M protein produced in each medium and the latter to see whether they would become typable. Growth media were Todd-Hewitt Broth (BBL), 10 ml (TH); Todd-Hewitt Broth plus 2.2% sucrose, 10 ml (TH &S); Todd-Hewitt Broth, 40 ml (TH 40); and 0.5% yeast extract (Difco), 10 ml (Y). Each tube was inoculated with a 3-mm loopful of a broth culture of the strain being tested, and was incubated at 37 C for 18 hr. Acid extracts for serological grouping and typing were prepared according to the method of Swift et al. (J. Exptl. Med. 76:127, 1942). Extracts of typable strains were diluted 1:1, 1:2, 1:4, and 1:8 in 1 N saline before testing with their homologous antisera, to obtain an estimate of the quantity of M protein. Nontypable strains were tested with 34 types of antisera available from the Communicable Disease Center, At-