Laboratory evaluation of a rapid four-hour serological grouping of groups A,B,C, and G beta-streptococci by the...

Grouping of beta-hemolytic streptococcal isolates by staphylococcal coagglutination was performed with the Phadebact Streptococcus Test to determine whether such isolates could be accurately grouped serologically with 4 h after examination of the primary isolation plates. Of 132 clinical isolates, 131 were correctly grouped by the Phadebact method using the Lancefield precipitation method as the accepted standard. Of the correctly grouped streptococci, 119 were definitively grouped within 4 h after examination of the primary plates, and the remaining 12 isolates were grouped within 24 h. Since the Phadebact Streptococcus Test contains coagglutination reagents for groups A, B, C, and G, those isolates that failed to react were considered as positive for groups other than the four included in the test system. There were 23 such isolates in this study. Lancefield grouping of these isolates indicated that nine were group F, five were group D, and the remaining nine were not groupable with the Lancefield reagents employed in this study. The one Phadebact "failure" involved an isolate that produced a 4 + reaction with the Phadebact group A reagent and a 4 + reaction with Lancefield group F reagent.