Identification of clinically relevant viridans streptococci by analysis oftransfer DNA intergenic spacer length polymorphism

The utility of PCR analysis of transfer DNA intergenic spacer length polymo rphism (tDNA-ILP) for the identification to the species level of clinically polymorphism (tDNA-ILP) for the identification to the species level of cli nically relevant viridans streptococci was evaluated with a collection of r eference strains of 15 species of the salivarius, anginosus, mitis and muta ns rRNA homology groups. PCR products generated by using fluorescent, outwa rdly directed, consensus tDNA primers were analysed by electrophoresis on d enaturating polyacrylamide gels and by laser fluorescence scanning. Eleven species showed specific and distinct tDNA patterns: Streptococcus cristatus , Streptococcus gordonii, Streptococcus oralis, Streptococcus mitis, Strept ococcus pneumoniae, Streptococcus sanguinis, Streptococcus parasanguinis, S treptococcus anginosus, Streptococcus mutans, Streptococcus criceti and Str eptococcus ratti. Indistinguishable patterns were obtained among two groups of species: Streptococcus vestibularis and Streptococcus salivarius on the one hand and Streptococcus constellatus and Streptococcus intermedius on t he other. S. mitis strains produced heterogeneous patterns that could be se parated into three groups: a group containing S. mitis biovar 1 and two S. mitis biovar 2 groups, one of which clustered with S. parasanguinis strains while the other showed patterns unrelated to other species. These results agree in part with protein electrophoretic analysis showing that S. mitis b iovar 2 strains belong to several streptococcal taxa. In conclusion, PCR an alysis of tDNA-ILP holds promise for rapid identification of viridans strep tococci that are difficult to identify by phenotypic tests.