Did you know that ions of several metals including brass, copper, aluminum, iron, lead and silver are antimicrobial, that is, they kill bacteria.
In fact brass is the the most antimicrobial of them all. According to the Wikipedia entry on the subject:
Brass doorknobs disinfect themselves in about eight hours, while stainless steel and aluminum knobs never do. Brass doorknobs therefore tend to be more sanitary than stainless or aluminum doorknobs.