Ethanol and bacteria: To kill or not to kill?

That is the question.

There is a commonly held belief that ethanol “moves” rather than killing bacteria.  Is this really the case?  Does ethanol move bacteria without killing it?  Or does it move around the bacteria it has killed because you are rubbing it over a potential injection site.  As in, yeah it’s moving around bacteria – DEAD bacteria.  I decided to investigate further because I am a little sceptical of this idea that ethanol doesn’t kill bacteria.

The CDC lists some of the many bactericidal (including Gram positive and Gram negative species of bacteria), fungicidal, and virucidal effects of varying concentrations of ethyl alcohol and isopropyl alcohol [1].  In fact, they specifically state, “alcohols are rapidly bactericidal rather than bacteriostatic” [1].  They do note that alcohol is ineffective against bacterial spores [1].  Two types of spore-forming bacteria are the Clostridium and Bacillus bacteria.  These bacteria can cause major problems if present on invasive medical equipment and as such this is not an ideal sterilization method for surgical equipment [1].  

However, this is beside the point.  The point being that alcohol DOES kill.  It kills bacteria.  It kills fungi.  It kills viruses.  It kills people, but again that is way off track.  (Also, ironically enough, chronic alcoholics have increased susceptibility to certain infections [For an old but interesting study see 2].)

Now that we’ve established that alcohol does kill bacteria, how does it accomplish this?  Our lab language for this mechanism is that it kills like a hammer.  Although the detailed mechanism seems to be unknown, it is probable that cell membrane disruption and protein denaturation are the methods by which alcohol kills bacteria, which sounds slightly more scientific but less exciting [1, 3].  The ensuing disruption in membrane and metabolism results in cell lysis [3].

So next time somebody tries to tell you that alcohol only moves, rather than killing bacteria remember this: Those bacteria are being killed with a hammer people!

Disclaimer: There are instances in which other disinfectants or sterilization methods are needed and for good reason.  However, the sole purpose of this post is to dispute that alcohol only moves.  I hope you were moved to consider this point.

  1. CDC. Guideline for disinfection and sterilization in healthcare facilities. Healthcare Infection Control Practices Advisory Committee (HICPAC). 2008.

  2. Johnson, W., Stokes, P. & Kaye, D. The effect of intravenous ethanol on the bactericidal activity of human serum. Yale Journal of Biology and Medicine. 1969;42:71-85

  3. Mcdonnell G, Russell AD. Antiseptics and disinfectants: activity, action, and resistance. Clin Microbiol Rev. 1999;12(1):147-79.