Evaluation of three commercially available test products for serogrouping beta-hemolytic streptococci

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Abstract
Three .beta.-streptococci serogrouping kits, Phadebact, SeroSTAT and Streptex, were evaluated as to their sensitivity, accuracy and suitability as methods for serogrouping streptococci in a clinical microbiology laboratory. The majority of the primary isolates examined by the various methods associated with each of the 3 kits were correctly identified. The Streptex direct mixed-culture procedure was more often associated with the observation of cross-reactivity than with the direct procedures of the other 2 kits, which did not employ mixed growth cultures. The Streptex kit was associated with more false-negative responses than those determined by the other 2 kits under evaluation. These results appeared to be due to the relatively poor sensitivity of the Streptex grouping reagents. The Streptex test procedures required more labor than the other kit procedures, requiring a 1 h enzymatic extraction step for the release of the group antigens. The SeroSTAT kit provided only a direct procedure and is limited in its application. The Phadebact procedures were the most versatile by providing not only a direct and a 24 h grouping procedure, but also by including a 4 h method that may be employed as required by the clinical microbiologist.