PCR for detection and identification of Streptococcus sobrinus

Oligonucleotide primers were designed based upon a comparison of the dextra nase gene (dex) sequences from Streptococcus sobrinus and S, mutans. The pr imers amplified a 1610-bp long DNA fragment on the dex gene by a PCR, The p air of primers was specific to S, sobrinus as the other members of the muta ns streptococci - S, mutans, S, downei, S, cricetus, S, rattus, S, macacae and S, ferus - gave no PCR products. Other grampositive oral bacteria (15 s trains of 10 species of cocci and 18 strains of 12 species of rods) and gra m-negative oral bacteria (3 strains of 3 species of cocci and 31 strains of 22 species of rods) also gave negative results in the PCR, The PCR procedu re was able to detect as little as 100 fg of purified chromosomal DNA or as few as 9 cfu of S, sobrinus NIDR6715, Seven clinical isolates of S, sobrin us were also positive in the dex PCR, This laboratory developed the S, muta ns-specific PCR (dexA PCR) method with the primers specific for a portion o f the dextranase gene of S, mutans Ingbritt, Primers for the dex and dexA P CR methods detected two species exclusively from the mutans streptococci. F urthermore, these two species were effectively differentiated by the specie s-specific amplicons with different lengths. The application of the PCR met hod to human dental plaque showed that the prevalence of S, sobrinus (83%) in oral cavities was higher than currently supposed (0-50%), These results suggest that the described PCR method is suitable for the specific detectio n and identification of human cariogenic bacteria, S, sobrinus and S, mutan s.