Strain-related acid production by oral streptococci

Acid production, in particular at low pH, is thought tb be an important eco logical determinant in dental caries. The aim of the present study was to d etermine the acid producing capability at different pH levels of 47 strepto coccal strains, representing 9 species, isolated from human dental plaque. The bacteria were grown until mid log-phase under anaerobic conditions and acid production was measured in a pH-stat system at pH 7.0, 6.0, 5.5 and 5. 0. At all pH values, the mean velocity of acid production (V-ap) by Strepto coccus mutans and S. sobrinus was significantly higher (p<0.01; ANOVA) than that of the other oral streptococci, including S. mitis, S. oralis, S. gor donii, S. sanguis, S. intermedius, S. anginosus, S. constellatus, and S. ve stibularis. However, the V-ap of some strains of S, mitis biovar 1 and S. o ralis, particularly at pH values of 7.0 and 6.0, exceeded that of some stra ins of S. mutans. The V-ap decreased with pH for all strains, but some stra ins of S. mitis biovar 1 and strains of the mutans streptococci maintained a relatively high rate of acid production. The results suggest that some st rains of S. mitis biovar 1 and S. oralis may play an important role in cari es development by modifying the environment in dental plaque to become favo urable for the succession of aciduric species. The study furthermore emphas ises the need for detailed species and biovar identification of oral strept ococci and for recognition of the significant physiological differences tha t occur within single species. Copyright (C) 2000 S. Karger AG, Basel.