Avoiding The Spread of Infection – In More Ways Than One

Monday, December 3, 2007

It's well known that a primary vector of disease is a germ-laden hand. Mano to mano, much misery in the land of the adenovirus is spread from a handshake. So what can you do when a sniffling colleague heads over to greet you at a holiday party?

Many carry small bottles of antimicrobial hand sanitizer during flu season. But Saint Joseph's University medical microbiology expert Michael McCann, Ph.D., says to think twice before reaching into your pocket. Instead, he advises thorough hand washing with conventional soap and warm water.

"The use of antimicrobials by the general public may be a literal case of over-kill," notes McCann. "Research suggests wide-scale application of these sanitizers promotes the evolution of drug-resistant strains of bacteria. Many contain chemicals like triclosan that specifically kill bacteria, but do not harm us. The problem is, triclosan can trigger 'selection.'"

McCann explains that selection occurs when conditions become favorable or unfavorable for individuals of the same species, based on genetic variation. In this case, if millions of bacteria are exposed to triclosan, it kills almost all of them.  But if one of those bacteria has a genetic mutation that enables it to survive the lethal chemical, then the application of triclosan will select for that individual. Only bacteria resisting the chemical survive.

Descendents of resistant bacteria also carry the mutation, which leads to the generation of large populations of resistant organisms. "This is exactly what has happened with antibiotics, and why strains of bacteria like MRSA are no longer susceptible to many commonly used antibiotics," he adds.

McCann says studies have shown sanitizers that use alcohol -- ethanol and/or isopropanol -- are much more effective at killing microorganisms and inactivating viruses than triclosan. Further, there does not seem to be a mechanism by which bacteria and other organisms can evolve resistance to alcohols -- another reason to use these products.

So if you can't get to soap and water quickly at the holiday party, it's safe to break out the hand sanitizer -- as long as it contains alcohol.

McCann, a professor of biology and associate dean of the College of Arts and Sciences, can be reached for comment at mmccann@sju.edu or 610-660-1823, or by calling the Office of University Communications at 610-660-1222.

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