Exactly. It changed. Just as humans "de-volved" the highly useful trait of malarial resistance through sickle cell anemia. The end result is degradation of higher life forms, hence the term "devolution".
"Or did God (ahem - the designer) have to intervene mysteriously in order for the antibiotic resistance to develop?"
Maybe He did. Maybe He didn't. Maybe the Bible is right: Maybe physical corruption of the creation is related to the moral corruption of creation.
How do you explain how antibiotic resistance arises in a population?
Resistance existed in some of the bacterial organisms, somewhere, somehow. Otherwise, by definition, they'd all be dead. The ones that didn't have resistance died. You can't "develop resistance" in dead organisms. Anyway, are "more destructive parasites" the definition of fitness?"
And this is all beside the point, because it still doesn't explain how you got a brain. Which is what Big E-volution is supposed to explain. You don't need that brain to propagate (your definition of "fitness"), you could have easily done it as a bacterium. And a lot more prolifically.
Supposing that a god of the gaps had to mutate the bacteria for it to develop antibiotic resistance is a useless postulate, one that leads nowhere and to nothing, to no further discovery or useful application. And really, there is no need to invoke divine intervention when genetic variation created through error prone DNA polymerase and natural selection of that variation is both necessary and sufficient to explain this type of change.
Supposing that natural selection of (newly created) genetic variation is at work leads to the inescapable conclusion that one should finish their regimine of antibiotics rather than stop taking them once they feel better - and that one should not leave unused antibiotics on the shelf to age and self-prescribe. Once again showing how creationism is useless while science is of use.
Why do bacteria have a stress induced gene for error prone DNA polymerase? Because they need to “de-evolve” in response to stress?
And no, dead bacteria do not evolve - that is why subjecting bacteria to a stressful but not lethal dose of antibiotics - usually through improper use - is how resistant strains can arise.