OBJECTIVETo establish a quick and reliable method to identify Streptococcus oligofermentans, a new species of oral streptococci.

METHODSWith two-step PCR, a pair of the 16S rDNA-specific primers of Streptococcus oligofermentans and a pair of primers of lactate oxidase gene (lox) were used to amplify the gene fragments from the genomic DNAs of 11 strains consisting of 9 species of the pure culture of oral streptococci. Pooled plaque samples from 9 caries-free volunteers were cultured on a selective medium of MSA with erythromycin and tentative strains of Streptococcus oligofermentans were isolated. The isolates were further identified by the two-step PCR and finally confirmed by 16S rDNA sequence analysis.

RESULTSWith the two-step PCR, the two gene fragments were only amplified from the three identified strains of Streptococcus oligofermentans, but not the rest of 8 strains of oral streptococci. Isolates from the dental plaque of caries-free volunteers were identified as Streptococcus oligofermentans by PCR and then further confirmed by 16S rDNA sequence homology analysis.

CONCLUSIONSStreptococcus oligofermentans could be identified by the two-step PCR approach with the specific 16S rDNA primers and lactate oxidase gene primers.