A comparative study of glucose and galactose uptake in pure cultures of human oral bacteria, salivary sediment and dental plaque

The ability to utilize glucose and the weaker sugar acidogen, galactose, was surveyed in salivary sediment, pooled dental plaque, and in pure cultures of the bacteria that numerically comprise most of the bacteria in these mixed microbial systems. Except for a veillonella isolate, which showed no uptake of either sugar, glucose was utilized more rapidly than galactose by the 27 pure cultures tested and by both sediment and plaque. This sugar difference was also seen for two other measures of glycolysis, formation of acid and previously studied ability to produce an acidic pH. Rates of uptake of the two sugars by individual pure cultures varied considerably. Generally, the Gram-positive bacteria utilized glucose and galactose at rates similar to those seen with salivary sediment and dental plaque, whereas the Gram-negative cultures tested showed much slower uptakes. Bacteria previously identified as arginolytic had lower glucose and galactose uptake rates than similar non-arginolytic micro-organisms. This, together with the ability to produce base from arginine, would explain their tendency to produce a less acidic pH. In pure culture mixtures, uptakes were generally predictable and indicated an averaging effect. When the microbial compositions of salivary sediment or dental plaque were altered by mixing with pure cultures of high glucolytic activity, such as many of the Gram-positives, glucose uptake was enhanced. The opposite was observed when the less glucolytic Gram-negative bacteria were similarly incorporated. As well as determining the glucose and galactose uptake rates of the various bacteria that collectively comprise the bulk of the salivary sediment and supragingival plaque microfloras, this study has shown how variation in microbial composition affects sugar uptake rates and has indicated how microbial composition could be manipulated to produce dental plaques with different capacities to ferment sugars and presumably different cariogenicities.