One comment. With bacteria, resistance is to specific (or multiple) antibiotics. This doesn't mean necessarily that the strongest bacteria in general terms get selected. For example MRSA tends to affect people who for some reason have weakened immune systems because healthy people do a decent job of fighting it off.
Good point. My use of the word "strongest" was definitely misleading, but I am not convinced it is always the case that there isn't a relatively low dimensional definition of "strong" in this sense.
I think (and if I'm wrong someone please correct me) that adaptations the bacteria evolve are specific features to specific pathways that they have for removing toxins (to a bacteria an antibiotic is a strong toxin).
