The mechanism by microbes are killed varies with the agent or agency employed against them. If sufficient heat is supplied, the microbial cell walls are ruptured, and the cellular proteins coagulated. Chemicals affect microbes in various ways, depending upon the chemical: some actually disolve the cell wall; others, such as bleach, will oxidize the organism, in effect doing the equivalent of buring it up; others will affect the microbe at the electronic level by realeasing free radicals that actually invade the microbe and disrupt its internal processes. In the body, microbes are attacked by whilte blood cells that "eat" the microbial cells or isolate them. (It's a bit more complicated than that, but that's the simple answer.) Antibiotics are chemicals which generally attck the protein in the microbial cell and render it unable to function.
