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How does soap effect bacteria?

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

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How does soap effect bacteria?

Postby SOSInNeedOfJesus » Sat Jun 23, 2007 4:51 pm

We all know that soap removes dirty shtuff from our hands/feet/body/etc.
But how does it scientifically work?

I know about a experiment where people wash their first finger once with and second finger twice with and third finger three times with soap and the fourth finger with rubbing alcohol. The results are that the soap doesn't remove that much of bacteria, so does that mean soap doesn't work?
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Postby mith » Sat Jun 23, 2007 6:12 pm

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Postby ninetails » Fri Jul 06, 2007 1:30 pm

ok to get an answer for this experimental observation let's first look into how soaps work.

Soap molecules have two special sites on their structure.

one is a hydrophylic end [ S ]- can and will stick to water molecule.

second one is a hydrophobic [ P ](can't stick to water molecule or liphophilic(can and will stick to oil molecule) end.

Most dirt is oil based. That is its a greasy substance. If you don't have oil mixed with the dirt, then you don't need soap, plain water would be sufficient.

When you take the greasy finger and insert it in a soultion containing foam made out of soap water, the following reaction takes place.

H20--SOAP--OIL--SOAP--H20

As you can see the oil is completely surrounded by water and soap, which aids in complete removal of the oil based dirt after thorough rinsing. The oil has no place to hold onto other than water and soap right.

Now coming to the experiment.
The cell wall of bacteria is a complex one. Added to that, these guys have a cell membrane below that.
Soap cannot remove the bacterial cell that has stuck on to the skin using various mechanisms that it has unlike dirt which is simple stuck there because it is greasy.Grease or oil is stuck to the skin because of the laws of phsyics, surface tension.
Flagella and pilli(thread like structures present on the cell membrane) help it to attach strongly to the skin surface.

Google for a picture of flagella and pilli for a clear picture.


Alchohol: Think they would have used ethanol for the experiment.
This guys is different, he is a dehydrating agent leaving the surface dry and he can destroy the cell wall of microorganisms, causing the inner contents to flow out leading to cell death. It's used in labs as a sterlizing agent.

Soap ain't as powerfull as ethanol for sterlizing purpose. There used to be a rumour in our lab, someone noticed bacterial growth on a bar of soup left in the bin :twisted:. heh come on its another story.

I did be glad is someone could post the detailed chemistry behind the reaction and also the reason for the destruction of cell wall of bacteria by ethanol.

:)
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WoW Thanks

Postby SOSInNeedOfJesus » Sun Dec 09, 2007 5:00 am

Dang, you know your stuff!

Thanks muchos!
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