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Although the pathogenesis of Streptococcus oralis may be different from that of other viridans group streptococci, S. oralis shares a high degree of DNA sequence similarity with these streptococci. As a result, discrimination of S. oralis from its close relatives has long been considered difficult. This study was conducted to find specific genes that allow for the in vitro identification of S. oralis, but not other oral commensals. Four hundred ninety S. oralis clones obtained by suppressive subtractive hybridization were used for Southern hybridization, and positive clones were sequenced. Of 5 S. oralis-specific clones, newly designed primer sets based on the glucosyltransferase regulatory gene amplified genomic DNA only from S. oralis strains, but not from any of the other 125 strains tested. Our findings may be useful for the future development of efficient diagnostic tools for the rapid identification and differentiation of S. oralis from other oral streptococci strains.

Streptococcus pneumoniae is the main etiologic agent of pneumonia worldwide. Because the members of the viridans group streptococci share a high degree of DNA sequence homologies, phenotypic and genotypic discriminations of S. pneumoniae from the viridans group are difficult. A quantitative real-time PCR assay targeting the capsular polysaccharide biosynthesis gene (cpsA) was developed as a species-specific detection tool for S. pneumoniae. The specificity was evaluated using genomic DNAs extracted from 135 oral cocci strains. Twenty-seven S. pneumoniae strains tested positive, whereas 108 other strains including Streptococcus pseudopneumoniae, Streptococcus mitis, and Streptococcus oralis did not show a specific signal. The linear regression of standard curves indicated high correlations between the log numbers of S. pneumoniae cells and the C(T) values (R(2)=0.99). The minimal limit of detection was 32 fg of purified genomic DNA, equivalent to 14 genomes of S. pneumoniae. This new real-time PCR method may be very useful as a rapid and specific tool for detecting and quantifying S. pneumoniae.

Background Streptococcus pseudopneumoniae, is a novel member of the genus Streptococcus, falling close to related members like S. pneumoniae, S. mitis, and S. oralis. Its recent appearance has shed light on streptococcal infections, which has been unclear till recently. In this study, the transcriptome of S. pseudopneumoniae CCUG 49455T was analyzed using the S. pneumoniae R6 microarray platform and compared with those of S. pneumoniae KCTC 5080T, S. mitis KCTC 3556T, and S. oralis KCTC 13048T strains. Results Comparative transcriptome analysis revealed the extent of genetic relatedness among the species, and implies that S. pseudopneumoniae is the most closely related to S. pneumoniae. A total of 489, 444 and 470 genes were upregulated while 347, 484 and 443 were downregulated relative to S. pneumoniae in S. pseudopneumoniae, S. oralis and S. mitis respectively. Important findings were the up-regulation of TCS (two component systems) and transposase which were found to be specific to S. pseudopneumoniae. Conclusions This study provides insight to the current understanding of the genomic content of S. pseudopneumoniae. The comparative transcriptome analysis showed hierarchical clustering of expression data of S. pseudopneumoniae with S. pneumoniae and S. mitis with S. oralis. This proves that transcriptional profiling can facilitate in elucidating the genetic distance between closely related strains.