Inhibition of streptococcal growth, F-ATPase and pyrophosphatase by diphosphonates

1-Hydroxyethane-1,1-diphosphonate (EHDP) and a variety of other diphosphonates, and also pyrophosphate, at millimolar levels were found to inhibit the growth of Streptococcus mutans GS-5. Inhibition appeared to be due mainly to chelation of Mg2+ and could be readily reversed through addition of Mg2+, or less effectively, by other divalent cations. The trianionic forms of the diphosphonates or pyrophosphate were more effective inhibitors than the dianionic forms. Diphosphonates and pyrophosphate did not inhibit glycolysis by S. mutans, assayed in terms of glucose utilization, or arginolysis by Streptococcus rattus FA-1, assayed in terms of ammonia production. However, they did act as buffers to moderate pH changes. Diphosphonates also were inhibitors of the F-ATPase of S. mutans by complex mechanisms only partly reversible with divalent cations. They also were inhibitors of the pyrophosphatase of the organism. However, intact cells were impermeable to the compounds, and inhibition of cytoplasmic or membrane enzymes did not appear to be involved in growth inhibition.