Inhibition of commonantigen fluorescence in grouping streptococci by the fluorescent antibody method.

The fluorescent antibody method of Coons and Kaplan (1950) has led to numerous studies of its practical application, many directed to the problem of rapid and accurate identification of microorganisms (Goldman, 1953, 1957; Moody, Goldman, and Thomason, 1956; Thomason et al., 1956, 1957; LaBrec, Formal, and Schneider, 1959; Winter, and Moody, 1959). Moody, Ellis and Updyke (1958) showed that serological grouping of f8-hemolytic streptococci was possible by specific fluorescent antibody staining of smears prepared from cultures. Rapidity, economy, and ease of performance were cited as advantages of this procedure over the conventional precipitin test. Because of its timeconsuming nature, routine use of the latter has been impracticable in most laboratories except for special investigations despite evidence that infections with group A streptococci may be forerunners of rheumatic fever and its sequelae. Therefore, a method which permits rapid, accurate determination of the presence of group A hemolytic streptococci in routine throat specimens is of considerable importance. This report deals with application of the fluorescent antibody technique to a large volume of routine cultures from presumed streptococcal infections submitted to a state health laboratory, with the problem of preparing and standardizing the reagents involved and with ancillary means of demonstrating, within 24 hr after receipt, the presence of group A streptococci in specimens when present in sufficient numbers to justify a logical assumption of etiological significance. Primarily it deals with rapid differentiation by inhibition of common antigen fluorescence among serological groups A, C, and G. The procedure