What's an Agar Plate?

I've already shared this with several of you, but since I'm in the throes of yet another cold virus, I thought it was worth mentioning again.

In a letter to the editor published in the March 2006 issue of Emerging Infectious Diseases, Reynolds et al describe a study they conducted that reinforces the accepted fact that hand sanitizer gels must contain at least 60% ethanol or isopropanol (alcohol) to effectively eliminate bacteria. However, the authors note that this important qualifier is not usually conveyed by nonhealthcare groups.

You can read the complete letter on the Emerging Infectious Diseases Web site, but the upshot is that they describe a study wherein subjects placed their hands on an agar plate in the morning, then washed their hands using one of several treatments, including tap water, 40% ethanol, commercial sanitizer with 40% alcohol concentration, or commercial sanitizer with 62% alcohol concentration. After treatment, the subjects placed their hands on a fresh agar plate.

Only the sanitizer with 62% alcohol concentration produced a decrease in bacteria on the hands. In fact, the sanitizer with 40% alcohol produced a more even distrubtion of bacteria on the agar, probably because the movement dispersed the bacteria without killing it.

So, check that sanitizer gel you're using.

And if you're one of those germy people (you know who you are) who makes a pretence of handwashing by running the tap for 2 seconds (sans soap) in the public restroom, don't bother.

As for me, I'll be the person behind you, washing her hands with soap and water for 10-15 seconds (the time it takes to sing "Happy Birthday"), using her elbow to push open the bathroom door, and then sanitizing my hands with gel containing at least 60% alcohol concentration.*

And does anyone know where I can get an agar plate?


Reference:
Reynolds SA, Levy F, Walker ES. Hand sanitizer alert [letter]. Emerg Infect Dis. 2006 Mar. Available from http://www.cdc.gov/ncidod/EID/vol12no03/05-0955.htm


*Yes, I know--if I do all that, why do I still have a cold? I'm not sure, but I haven't lost faith yet.