Rapid identification of pregnant women heavily colonized with group B streptococci

Pregnant women admitted to Tampa General Hospital, Tampa, Fla., were cultured for group B streptococci (GBS). Culture swabs were placed into enriched, selective Todd-Hewitt medium and were quantitated for GBS. The broth cultures were tested by slide coagglutination before incubation and after 5 and 20 h of incubation. Fifty-four (27%) of the 201 maternity patients cultured were positive for GBS and were identified as such by slide coagglutination. A strong correlation was found between the magnitudes of colonization and the times required to identify the broth cultures as GBS positive. Cultures from mothers heavily colonized (mean concentrations of 3 X 10(4) GBS per culture swab or greater) were identified after 5 h or less of incubation. Mothers lightly colonized with GBS (mean concentrations of 2 X 10(2) GBS per culture swab) were identified only after their broth cultures had been incubated for 20 h.