Taxonomic study of "tufted mitior" strains of streptococci (Streptococcus sanguinis biotype II); Recognition of a new genospecies

The taxonomic position of tufted strains of streptococci, phenotypically re sembling Streptococcus mitis and previously referred to as 'tufted mitior' was investigated. By 16S rRNA sequence analysis, it was clear that the "tuf ted mitior" strains belonged to the mitis group of species within the genus Streptococcus. It was confirmed that these strains were taxonomically inde pendent at the species level, sharing less than 43% DNA-DNA similarity with all established species of the mitis group. However biochemical test data obtained, using three commercial identification kits (Rapid ID32 Strep, STR EPTOGRAM, and Biolog GP-plate) together with in-house biochemical tests emp loying 4-MUF-linked fluorogenic substrates did not reveal sufficient differ ential tests with which to identify the "tufted mitior" strains unequivocal ly. From these data, we conclude that these "tufted mitior" strains represe nt a new taxon within the mitis group of the genus Streptococcus, and propo se that they should be considered as a genospecies until differential pheno typic characteristics are found for their identification.