An in vitro study of bacterial response to inert and reactive metals and to methyl methacrylate.

The clinical use of inert materials for internal fixation and joint replacement devices is increasing rapidly; studies on the effect of these materials on bacteria and host resistance to infection have not kept apace. Any substance placed within the body may interfere with host-parasite interaction, either by its physical presence or by physiochemical activity at its interface with the surrounding tissue. Either mechanism, by altering the normal host defense mechanism, may promote or retard bacterial growth. Bacterial growth may also be altered if a trace element essential to or inhibitory to the bacteria or an element that antagonizes or potentiates humoral antibacterial systems is leached from the substance. We have tested bacterial growth and inhibition in vitro in the presence of substances used as implant materials: surgical silver, iron, zinc-coated galvanized iron, aluminum alloy, stainless steel, Vitallium, and methyl methacrylate. Our results showed: 1) metals that have low grades of tissue reactivity and little bacteriotoxic effect provided a framework along which bacterial growth and propagation occurred; 2) metals that have higher levels of cellular reactivity, specifically aluminum and galvanized wire, caused selective bacterial toxicity. The in vitro response of bacteria to methyl methacrylate was similar to that of Vitallium and other inert substances, i.e., growth and propagation were abundant adjacent to methyl methacrylate. These studies led us to speculate that, if similar phenomena occur in vivo, bacterial growth and dissemination might be increased when an inert implant material was used and decreased when the implant material was more reactive.