Utilization of glucose and lactic acid by salivary sediment

Abstract

The pH of suspended salivary sediment (SSS) was compared during 4 hr incubation at 37 °C with either low levels of glucose or molar concentrations of lactic acid twice that of the glucose. The pH changes which resulted were similar to those observed by Stephan and Hemmens (1947) with the same substrates in a bacterial system consisting of a medium designed to simulate the buffering properties of saliva and a pure culture of a sarcina isolated from dental plaque. Changes in sediment carbohydrate in the salivary sediment system also were determined with each substrate and related to the pH. With glucose, as the pH fell and subsequently rose, sediment carbohydrate correspondingly rose and fell. With lactic acid, the pH progressively rose from an initial low level; sediment carbohydrate initially increased and decreased slightly and then sustained during the 4-hr experimental period a slight increase relative to a water control. Lactic acid was an intermediate not an end product of glucose metabolism and did not appear to be a substrate from which significant amounts of sediment carbohydrate could be formed. In this study, lactic acid served as a “marker” of the stoichiometric conversion of glucose to lactic acid. Formation of sediment carbohydrate from glucose prevented the pH from reaching as low a minimum as would have been reached had no storage occurred.