Comparison of three methods for identification of Streptococcus milleri group isolates to species level

A collection of 180 clinical isolates of Streptococcus milleri group were identified to species level using two phenotypic methods (a commercial system and the reference method based on differential phenotypic reactions) and a genotypic method (hybridisation of the 16S rRNA gene with species-specific probes) in order to evaluate the performance of the respective methods. A high level of agreement (80%) was observed between the results of the reference method and the genotypic method. The highest level of agreement was found for the species Streptococcus anginosus (83%), a high level of agreement (76%) also being achieved for Streptococcus constellatus and Streptococcus intermedius. The sensitivity of the commercial system compared to the genotypic method was 76% overall, but it was low (57.5%) for Streptococcus intermedius. Twenty-five strains belonged to the recently described CI strains.