A Problem of Species Determination Using Housekeeping Genes in the Streptococcus anginosus Group

For identification of three species categorized in Streptococcus anginosus group (SAG), genotyping employing multiplex PCR for detection of species-specific genes has been widely used. We wondered whether possession of the specific genes correlated to differentiation of housekeeping genes, with an attempt to obtain more information on genetic background of clinical isolates of SAG strains and to evaluate reliability of the multiplex PCR. We therefore determined nucleotide sequences of some housekeeping genes of 52 SAG isolates from healthy volunteer to investigate whether the sequences phylogenetically corresponded to the identification by the multiplex PCR. The phylogenetic trees drawn with all of the sequences of 16S rRNA, sodA, groEL and rpoB were found to clearly correlate to species identified by the multiplex PCR. Interestingly, phylogenetic tree drawn only with single housekeeping gene often did not match with the species identified by the multiplex PCR. Our analysis implies even housekeeping genes can have their sequence varieties as independent manner from presence of species-specific genes in SAG strains, and the choice of housekeeping genes for the phylogenetic analyses may result in failure of the species identification.