Rapid slide coagglutination test for identifying and typing group B streptococci

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Abstract
A Cowan I strain of Staphylococcus aureus was labeled with group B streptococcal grouping or typing antiserum. These antibody-labeled reagent cells (ARC) were used in a slide coagglutination test to identify and type group B streptococci from blood agar plates. All streptococci were also identified by the standard Lancefield capillary precipitin test. In a blind study, all 141 group B streptococci were correctly identified by the coagglutination grouping test. None of the 148 non-group B streptococci caused agglutination of ARC. The coagglutination grouping test required an acid extract prepared from only 4 colonies and could be completed < 30 min after colonies were removed from plates. The coagglutination typing test correctly identified 98.6% of the types of the 141 group B streptococcal strains tested. At least 88.6% of these streptococci could be typed directly from blood agar plates within 5 min by the coagglutination typing test. The remaining 11.4% of the group B streptococci were acid extracted (< 30-min procedure), and the extract was used for coagglutination typing. Coagglutination typing can be performed with only 4 colonies. The coagglutination grouping and typing tests are inexpensive, rapid, reliable and easy to perform.