I used 95 % ethanol to disinfect Pseudomonas aeruginosa biofilms from titanium discs and compared it to disinfection with water and hydrogen peroxide. The strange thing was that when examining in SEM, roughly ten times more bacteria was present in the ethanol treated samples than the water treated samples hydrogen peroxide treated samples showed no bacteria. Metabolic activity assay showed however more bacterial activity from the water treated samples than the ethanol treated, hydrogen peroxide showed least. Anyone have any theory why ethanol seamed to increase the bacterial biofilm compared to water? Ethanol are regarded as an effective disinfectant on bacteria.

  • $\begingroup$ 95% Ethanol does not work as a disinfectant. You need to dilute it to around 70% to be effective. $\endgroup$
    – Chris
    Commented Oct 5, 2017 at 8:27
  • 1
    $\begingroup$ @Chris while that is true, wouldn't you still expect it to be better than water? $\endgroup$
    – arboviral
    Commented Oct 5, 2017 at 9:48

1 Answer 1


@Chris is right. ~70% ethanol is the way to go.

From a discussion here :

The effectivity of ethanol as e.g. desinfectant or antiseptic agent depends on the concentration of ethanol-water-mixture: An ethanol percentage of 50-80% destroys the cell wall/membrane of bacteria by denaturing their proteins and dissolving their lipids (effective against most bacteria, fungi and some viruses; ineffective against bacterial spores). Therefore, the ethanol has to pass the bacterial membrane/wall to get into the bacteria - if you use 100% ethanol instead, the bacteria get 'sealed' and they will survive... An other mechanism is the high osmotic pressure of ethanol/water-mixtures; and the 70% has the highest one.

By using a high ethanol concentration, you're effectively creating a layer of coagulated protein on the surface of the biofilm, "sealing" the bacteria in below that top layer.

As to why water seemed more effective than alcohol, I would venture a guess that some of the bacteria from the biofilm was flushed off. Maybe check the water for bacterial count to verify? :)


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