Macrorestriction fingerprinting of "Streptococcus milleri" group bacteria by pulsed-field gel electrophoresis

Although isolates of the "Streptococcus milleri" group (SMG) of bacteria ar e regarded as members of the commensal microflora of the body, they are fre quently encountered in purulent infections from a range of body sites. The genetic diversity of 91 epidemiologically unrelated SMG isolates (including 37 commensal strains and 49 disease-associated strains) was analyzed by ma crorestriction fingerprinting (MF). The genomes were digested with SmaI and ApaI independently, and fragments were resolved by pulsed-field gel electr ophoresis. Similarities between banding profiles were determined, and strai ns were clustered on this basis into dendrograms. In common with other comm ensal species that have been examined by MF, considerable genetic diversity was revealed. In addition, the clustering of strains tended to support the current taxonomic position of this heterogeneous group. The present study has shown that MF is a powerful tool for characterization of SMG strains an d that its use is likely to be of great value in epidemiological and popula tion genetic studies of this group of bacteria.