Direct use of counterimmunoelectrophoresis in detection of group B streptococci in specimens containing mixed flora.

Isolation procedures for the group B streptococci were bypassed by applying counterimmunoelectrophoresis (CIE) directly to the broth containing the initial inoculum. A total of 458 tests were performed on 389 specimens received from 93 mothers and 81 babies. Of all tests, 19.4% were positive group B streptococci by the Lancefield precipitin method. Twenty hours of incubation were required to produce a positive CIE result in 54% of those specimens which were eventually proven a contain group B streptococci by Lancefield technique. There were no false positive CIE results. It is recommended that the initial broth culture be sampled and tested with CIE after an overnight incubation in those cases where another 24 h may be critical in terms of identifying the group B streptococci. A positive result with CIE can be clinically relied upon, but a negative result is indeterminate, and routine isolation procedures would need to be followed in that case.