how exactly does soap kill baceteria and germs?
Chief’s Domain - http://www.seas.ucla.edu/~ravi
While plain old soap might kill germs (ruin their day somehow) its real job is to aid in the mechanical action of rubbing your hands together to rub dirt, germs, and grease so you can rinse them off. That’s why you are supposed to take the time to make a lather and use one hand to rub the other and so forth.
Even for the other parts of your body, it is the rubbing of soapy hands or soapy face cloth that does the work.
Oh, I’m gonna keep using these #%@&* codes 'til I get 'em right.
In the December 1999 issue of Discover there is an article called “The Biology of Hand Washing”. http://www.discover.com/recent_issue/index.html
Soap, being a detergent, disrupts the lipid bilayer that encapsulates the bacteria. By solubilizing their membranes, the bacteria are ruptured and die. This is acheived more effectively, however, by the mechanical action of washing your hands, as Jois mentioned.
I used to rock and roll all night and party every day. Then it was every other day. Now I’m lucky if I can find a half an hour a week in which to get funky.
Sheesh Alphagene, you went WAY over my head on that one.
< giggle >
So I am blonde, gimme a break!
Well I’m a big fan of allowing the layman and laywoman to understand science so I’ll bring it down a notch for ya. 
Soap works by making fats and oils (also known as lipids) more soluble in water. In a very simplistic model, the outer surface of bacteria is made of lipid. By applying soap to that lipid surface, you are making it more soluble in water. Therefore it breaks up and dissolves. With the outer surface dissolved, the integrity of the bacterial structure is lost. Ta-da. Dead bug.
The shearing action of rubbing your hands together contributes to this process.
I used to rock and roll all night and party every day. Then it was every other day. Now I’m lucky if I can find a half an hour a week in which to get funky.
Alphagene is pretty well right. However, some bugs are more resistant to the detergent action than others. I’ve seen situations where the surface of soap (both liquid and solid) has been colonised by bacteria such as Pseudomonas. This is (forgive a simplified generalization please)because there has been a moisture film on the soap, and because bugs like Pseudomonas are very good at resisting cell membrane effects. The little dears (eg Ps. cepacia) can grow in deionised water with some effort, and go through a terminal membrane filter - 0.45 micron definitely, 0.2 occasionally.
For liquid soap the likeliest reason for the film is the dispensor was rinsed but not really dried and bacteria were able to colonise the wettest region (water droplets), adapting to the increasing soap concentration down the water film over time and repeated exposures and eventually being able to grow in the soap itself. (Did I hear you say “Where’s the evolution thread…”).
Same sort of thing for solid soap that’s been left totally wet for an extended period. Less common 'cos it usually dries out though.
The solution is not, repeat not, disinfectant soap for everyday household use, as that only makes the whole problem of bacterial resistance to anti-bug agents more widespread, and in the domestic situation they may in fact be less effective in cleaning. This is due in part to the inclsion of emollients to counter the fat-stripping effect on the skin, and the emollients will in turn require increased mechanical scrubbing.
Ordinary liquid and solid soaps will work just fine in the domestic setting if you heave them out if they look scummy.
Sorry - micro information always seems to sound tacky.