A Comparison Between four Serological Methods Used in the Identification of Streptococcus Agalactiae

Abstract

Four serological methods used for the identification of group B streptococci were compared; the Lancefield precipitin method using double diffusion in agar gel, co-agglutination employing commercial reagents, immunofluorescence staining and counterimmunoelectrophoresis. In two experiments using 177 and 673 streptococcal isolates the results indicated that the Lancefield technique is not as sensitive as the other three tests. The counterimmunoelectrophoresis test is very sensitive to minimal quantities of antigen and/or antibody, but tends to detect cross reactions with group C antigens. The other two methods showed the same number of positive reactions, but fewer false positives. The reasons for preferring either the immunofluorescence or the co-agglutination technique for the routine identification of group B streptococci are discussed, together with the comments from other authors who have made similar comparisons.