Rapid detection and identification of Streptococcus ratti by a species-specific PCR method

To establish a rapid and species-specific detection and identification method of Streptococcus ratti by polymerase chain reaction, two PCR primer pairs specific to S. ratti were designed on the basis of the nucleotide sequence of the dextranase gene (dex) of S. ratti ATCC19645(T). The primer pairs specifically detected S. ratti, but none of the other mutans streptococci (16 strains of 6 species). The PCR procedure was capable of detecting 1 pg of genomic DNA purified from S. ratti ATCC19645. We developed the Streptococcus mutans-, Streptococcus sobrinus-, Streptococcus downei- and Streptococcus salivarius-specific PCR methods (the dex PCR methods) with the primer pairs specific for a portion of the dex gene of each species. The mixture of these primer pairs including S. ratti (this study) successfully differentiated the five species of mutans streptococci by species-specific amplicons of different lengths. These results suggest that the present PCR method is suitable for the specific detection and identification of S. ratti, and that the mixture of primer pairs for the dex PCR methods is useful for species-specific detection and rapid discrimination of each species in mutans streptococci.