Rapid specific identification of group D streptococci by counterimmunoelectrophoresis

Clinical isolates of group D streptococci have been examined by counterimmunoelectrophoresis (CIE) to determine if this method might be of value in the rapid identification of the members of this group. Group D organisms identified by classical biochemical and serologic procedures were inoculated into Todd Hewitt broth and incubated at 37 degrees C. After 4 hours of incubation, free group D streptococcal antigen was detected in broth cultures from 70 of 70 group D enterococcal strains. Precipitin lines were readily visible immediately after electrophoresis in each case. In contrast, 10 nonenterococcal group D strains failed to produce detectable free group D antigen in the Todd Hewitt broth after 4, 24, or 48 hours incubation. Such antigen was detectable, however, after 48 hours incubation in Mueller Hinton broth containing 10 grams of glucose per liter. Representative strains of group A, C, G, and B streptococi, Streptococcus viridans and Streptococcus pneumoniae grown in Todd-Hewitt broth for 4 hours gave no precipitin lines when reacted against adsorbed monospecific group D antiserum. Group D antigen was also detected in broth cultures of direct swabs and in 18-hour blood culture broths. CIE appears to be a rapid and sensitive procedure for identification of the enterococcal strains of group D streptococci from clinical isolates.