Growth and acid tolerance of human dental plaque bacteria

Pure cultures of representative strains of cariogenic and non-cariogenic plaque bacteria were assessed for their ability to initiate and maintain growth in broths, adjusted to initial pH levels of 7.0, 5.5 or 5.0, and to produce lactic acid from sucrose or glucose in resting-cell suspensions at pH 6.5, 5.0, 4.5 and 4.0. Streptococcus mutans, Lactobacillus casei and Streptococcus faecalis showed greater acid tolerance than strains of Streptococcus sanguis, Streptococcus salivarius, Streptococcus mitis and Actinomyces viscosus. For all species, growth initiation in broth was more acid sensitive than lactic-acid production in resting-cell suspensions. These data confirm and extend previous observations that the species of plaque bacteria most closely associated with the initiation or progression of dental caries are more aciduric than non-cariogenic species.