Genetic competence is widespread among bacteria. Several competence (com) genes from a number of the oral streptococci have been characterized. Although conditions under which Streptococcus salivarius will develop genetic competence have not been identified, the presence of mosaic nucleotide sequences, such as those found for penicillin-binding proteins (pbp) conferring b-lactam resistance, suggest that this organism may develop competence. Objectives: In this study we sought to determine if homologues of known competence genes were present in the genome of S. salivarius. Methods: Genomic DNA from six clinical isolates of S. salivarius was analyzed for the presence of comA, comB, comC, comD, and comX homologues by Southern blotting and PCR analysis. PCR primers were based upon conserved regions within each of the genes of interest. Results: Amplicons for the comA, comB, comC, and comD genes were identified in each of the S. salivarius clinical isolates. No homologue of comX was found in any of the isolates tested. Southern blotting using probes generated from previously reported com genes confirmed the PCR results. Conclusions: Although S. salivarius has not been found to develop genetic competence under laboratory conditions, the presence of several com genes suggests that this organism may be capable of genetic exchange in vivo.

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