In-vitro acid production by the oral bacterium Streptococcus mutans 10449 in various concentrations of glucose, fructose and sucrose.

At intermediate and high concentrations, the results with the sugars were similar, with lactic acid as the main end product. Over 4 h, the pH fell from approx. 7 to 4. At low monosaccharide concentrations (2 mM glucose, 2 and 5 mM fructose), after an initial pH drop and period of lactic-acid production, evidence of pH rise and lactic-acid consumption were noted. This did not happen when sucrose was added to the bacteria. There was evidence of a heterolactic-acid fermentation pattern at low-sugar concentrations, lactic, acetic and formic acids being produced in similar amounts. The results suggest that, when low-sugar concentrations are present in dental plaque, Strep. mutans is capable of consuming previously-formed lactic acid.