E. Coli's resistance to 'antibacterial' hand washes

[Naggers]

So, I carried out an experiment to test the antimicrobial properties of 3 commercial hand wash solutions which claim to be antibacterial. It was a basic experiment for class, and was more about designing/planning the experiment rather than the actual data. However, I have to explain why each was more/less effective and I could do with a little help

 

Brief overview of the experiment:

 

Assay discs were submerged in Asda Essential Care Antibacterial Hand Soap(Store-brand cheap stuff), Carex Antibacterial Hand Wash and Palmolive Antibacterial Hand Soap, mixed with water to concentrations of 25%, 50%, 75% and 100%. The discs were placed on lawns of Bacillus megaterium and Escherichia coli.

 

Here is the results table showing the mean diameter (mm) of inhibitions zones created by the assay discs.

 

As you can see, All hand washes were more effective against the B. megaterium than the E. coli. I assume the active ingredients in the solutions work by disrupting the cell wall of the bacteria, would this be correct? If this is the case, I would have thought that the Gram-positive bacteria would be more resistant to this, due to the thicker peptidoglycan cell wall, and the Gram-negative E. Coli to be less resistant. As you can see however, this is quite the opposite of my results.

 

Am I going about this completely wrong? As you can probably tell I am barely a layman so any help is appreciated

[CharonY]

Actually they do not necessarily work on the cell wall. More commonly they act on cell membranes. In those cases the cell wall offers little protection as much may just diffuse through.

[Naggers]

Actually they do not necessarily work on the cell wall. More commonly they act on cell membranes. In those cases the cell wall offers little protection as much may just diffuse through.

 

I see, is there any reading you could point me to which would expand on this?

 

Thanks

[CharonY]

Regarding the antimicrobial substances I would suggest looking up the active ingredients (there are a huge number of those around, so they are bound to act differently).