[Morphologic and biochemical characteristics of viridans streptococci isolated from dental plaque]

The purposes of this study were to give the characteristics of viridans streptococci isolated from dental plaque, and the relationships with dental caries. We stained 69 patients' teeth on supragingival plaques (Plaque Index = 1) with the Pfiffer's reagent or FD&C RED#28 dye, then isolated 80 strains of oral streptococci from 69 patients. Cultures were grown in TSB, MS, and MSB media. A total of 80 fresh-isolated plaque streptococci, including strains of S. salivarius, S. sanguis, S. mitis, and S. mutans were identified on the basis of morphologic, dark field, SEM, and biochemical characteristics. All of the oral plaque streptococci were to be found in significant percentages in dental plaque. Patients who had caries harboured S. mutans more often (37/40) than patients without caries (7/29). S. mutans comprised the greatest percentage (37/69) of microorganisms encountered in caries' plaque, and there was an association between high counts of S. mutans and the presence of dental caries. Cultural and biochemical methods were used for the isolation and identification of the different species of S. mutans. The result indicated that biotype I were the most predominant species (50%) in dental plaque. Thus, it is possible to isolate, screen and identify unknown strains through the morphologic, darkfield, SEM, and biochemical characteristics of viridans streptococci isolated from human dental plaque. By means of the present methods for identification, we hold considerable promises for contributing to the prevention and diagnosis of dental diseases.