Antimicrobials: Healthcare's Silver Bullet Against HAIs?

The bacteriostatic properties of copper and brass were discovered two decades ago by Kuhn (1983) who discovered that older, tarnished brass hardware was actually more hygienic than newly installed stainless steel doorknobs and push plates. Kuhn used E. coli, Staphylococcus aureus, Streptococcus Group D and pseudomonas species to innoculate strips of metal, air-dried them for 24 hours at room temperature, inoculated them onto blood agar plates and incubated for 24 hours at 98.6 degrees F. The broths contained approximately 10 million bacteria/ml, a significant inoculum. Kuhn found that the copper and brass showed little or no microbial growth, while the aluminum and stainless steel produced a heavy microbial growth of all species. The test was repeated using several drying intervals, from 15 minutes to 24 hours. Kuhn noted that copper rid itself of some microbes within 15 minutes, while brass disinfected itself in seven hours or less, and newly scoured brass disinfected itself in one hour. Kuhn observed significant of all isolates on the aluminum and stainless steel strips as long as eight days after exposure. After three weeks, there was growth of all species except for Pseudomonas; scanning electron microscopy demonstrated that E. coli remained on the stainless steel but was eliminated on the brass.

Kuhn (1983) writes, “Culturing a stainless steel knob on a door between a burn unit and an intensive care unit, I found a multiply resistant Staphylococcus epidermidis with a susceptibility pattern identical to that found in the blood of a septic patient in the intensive-care unit. Cultures of wounds of several other patients yielded similar organisms. None of these observations prove cause, of course, but they ought to impress us with the need to take precautions, particularly in the presence of multiply resistant microbes ...We have known for years that certain metals are toxic to bacteria. It is the application of this knowledge to better infection control that warrants further attention.”