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"Here is a testable hypothesis for you. Working with Bacteria Strain XYZ, you hypothesize that there will be no change over time in its susceptibility to Drug ABC. That's the null hypothesis, SOP in biological science. But as you do your experiment, the data force you to reject the null hypothesis. The bacteria shows increasing resistance to the drug over time. The logical interpretation? The bacteria have been evolving so as to adapt to the environment to which you have placed them. Evidence of evolution--of the falsifiable variety."

False logic. The bacteria aren't changing. There's no evolution. Bacteria in the superset that have better pre-existing resistance to Drug ABC survive and propagate better than their peers in the test. Eventually, only those with resistance are left.

But there was no metamorphis. DNA didn't change in the survivors from pre-test to post-test.

You are both in error ~ in whole or in part ~ bacteria have such sophisticated immune systems they can BORROW GENES from other bacterial strains to protect themselves.

Don't make the error of confounding the individual bacteria cells with the real entity which is the "bacterial mat". In the end, after all the cutting and pasting, the mat will still look the same and all your tests for verifying one or the other bacterial species (if that's even an appropriate term for a critter that can borrow genes from other species) will continue to tell you what kind of bacteria it is ~ albeit with some markers that may or may not identify the "strain".

But there was no metamorphis. DNA didn't change in the survivors from pre-test to post-test.

Perhaps I wasn't clear. We're talking about over subsequent generations. To the contrary, the DNA of the gene pool does change over time.