Effect of trace metals on growth of Streptococcus mutans in a teflon chemostat

Correlations between the presence of certain trace metals in dental enamel or in drinking water and the incidence of human dental caries have been demonstrated; therefore, the effects of several trace metals on growth of the cariogenic organism Streptococcus mutans OMZ176 were determined. For continuous growth in a chemically defined medium (treated with Chelex-100 to lower trace metal contamination and supplemented with high-purity trace metal salts) used in a chemostat constructed of Teflon, S. mutans required input of carbon dioxide and supplementation with magnesium (126 microM) and manganese (18 to 54 microM). Addition of iron (3.6 microM) increased the level of steady-state growth by a factor of 2.8 (stimulation index [SI]); zinc at 0.4 microM nearly doubled equilibrium growth (SI = 0.9). Higher concentrations of iron and zinc (5.4 and 0.8 microM, respectively) were less stimulatory (SI values of 1.95 and 0.3, respectively). Small (but statistically significant) increases in steady-state growth were effected by cobalt (SI = 0.3 at 5.1 to 20.4 microM) and tin (SI = 0.4 at 5.1 to 10.2 microM). These data suggest nutritional requirements for these metals. Copper at a concentration of 0.16 microM was inhibitory. These results show significant effects of these metals on growth of S. mutans and may confirm epidemiological evidence suggesting a role for certain trace metals in the incidence of dental caries.