Evaluation of the rapid strep system for species identification of streptococci

The Rapid Strep system (API System S.A., Montalieu-Vercieu, France) was evaluated, without additional tests, in the identification of 209 streptococci. Organisms included 59 beta-hemolytic, 36 group D, 24 Streptococcus pneumoniae, and 90 viridans group streptococci. The Rapid Strep system correctly identified to species level 69.5% of the beta-hemolytic strains, 100% of the group D strains, none of the S. pneumoniae strains, and 84.5% of the viridans group streptococci. The method provided excellent identification rates of groups A, B, and D but failed to differentiate between groups C and G. The method for preparation of suspensions for the Rapid Strep system, as initially recommended by the manufacturer, was responsible for the failure to identify S. pneumoniae. This method was subsequently modified to yield a heavier inoculum; all 10 pneumococcal strains tested with the revised inoculum method were correctly identified. Good identification rates of commonly encountered viridans strains were found. The Rapid Strep system represents a worthwhile advance in streptococcal species identification, especially for group D and viridans strains.