Well the problem is that a lot of antibiotic resistance can be attributed to efflux pumps that literally pump the stuff out of the bacteria. So these are generalized resistance mechanisms that target a broad array of environmental stuff that might ordinarily kill a microbe. Here's a pretty well-cited paper on the issue, though it's rather old: http://aac.asm.org/content/45/2/428.short
I'm not a biologist, but I would assume that bactericides for external use can be much more aggressive than antibiotics that are injected in the organism; they are expected not to kill the patient altogether the bacteria.