Genetic approaches to the identification of the mitis group within the genus Streptococcus

The usefulness and reliability of partial sequence analysis of the manganes e-dependent superoxide dismutase gene (sodA), autolysin (lytA) gene amplifi cation and species-specific PCR based on the D-alanine:D-alanine ligase (dd l) gene for differentiating each member of the mitis group of the genus Str eptococcus was investigated. On the phylogenetic tree based on sodA partial sequences (366 bp) from 96 strains, including all species currently within the mitis group isolated in different geographic areas (mainly Japan and t he UK), eight well separated clusters were generated corresponding to recog nized species, and all strains fell into those clusters to which they had a lso been assigned by DNA-DNA hybridization. The Streptococcus pneumoniae su b-cluster was located within the Streptococcus mitis cluster, but the sodA gene of S. pneumoniae was very conserved and therefore could be separated f rom all other species examined. Furthermore, the lytA gene amplification ap proach could also be used to differentiate S. pneumoniae from other species . The species-specific amplification product of the ddl gene was successful ly detected in Streptococcus sanguinis and Streptococcus gordonii, but fail ed to be detected in some strains of Streptococcus oralis including the typ e strain and S. mitis. We conclude that the partial sequence analysis of th e sodA gene could be applied globally as a reliable and easy method for the accurate identification of all species currently within the mitis group.