An investigation of the bacteriostatic properties of pure metals.

The effect of 16 pure metals on the in vitro growth of a form of dental caries producing Streptococcus mutans was studied under both aerobic and anaerobic conditions. Cobalt and copper were consistently observed to be inhibitory. With less consistency nickel, titanium, iron, and vanadium also exhibited ability to inhibit growth of the organism. Bacteriostasis apparently is contingent upon the presence of a corrosion process. The bacteriostatic agent is of uncertain identity and could be a corrosion product or a process secondary to the occurrence of corrosion. Concentrations of metals after 6 days of electrochemical dissolution in the growth medium were measured via electron microprobe analysis and compared with the amount of inhibition which resulted. Threshold concentrations above which growth did not occur were identified. As measured by threshold concentrations, wide variability between metals exists in the ability to inhibit the growth, with cobalt being particularly effective at small concentrations. This implies a sensitivity on the part of the organism that is different for different metals. The threshold concentration varied between aerobic and anaerobic conditions. Streptococcus mutans appeared more resistant to the effects of the metals under anaerobic conditions even though little difference in the amount of corrosion was detected.