There have been millions of examples of bacteria developing new traits (antibiotic resistance) or losing traits (no longer able to live on some sugar) in a lab or in a sick patient. All of this is adaptation as well as evolution. Just like God designed it.
Pithy conclusions are excerpted below from the following article in ICR's Acts & Facts" September 2014 mail-out volume:
**********excerpts*******
"Darwin vs. Genetics: Surprises and Snags in the Science of Common Ancestry" (click here)
(1) . . . genetic hierarchies do not provide valid scientific evidence for evolution. Bona fide evidence for evolution must support Darwinism to the clear exclusion of design
(2) . . . the evolutionary hypothesis dramatically overestimates the actual genetic diversity within these species. Together, these results reveal that genetic differences are no friends of Darwinism; the Darwinists aren’t even getting the basic predicted counts right.
(3) . . . evolutionists predict that the human genome should be filled with junk DNA. The ENCODE project, a massive undertaking funded by the National Human Genome Research Institute, corralled a large amount of preliminary data that effectively refuted this hypothesis.
(4) Evolutionists have again assumed that pseudogenes are non-functional without doing any laboratory experiments. These tests have now begun to be performed, and recent results revealed that pseudogenes are quite likely functional.
Summary
Darwin was completely ignorant of the biological role of DNA when he penned his theory a century and a half ago. Now the evolutionary case from genetics is unravelling at multiple levels because it was never based on any direct evidence for common ancestry in the first place. Do the evolutionists have any lines of genetic evidence left? Evolution fails to predict either the absolute number or the function of genetic differences among species. This is remarkable since the supposed “engine” of evolutionary change is the genetic mistakes themselves. If evolutionists can’t even get their fundamental mechanisms to line up with their models, then why do they continue to present Darwin’s grand hypothesis as fact?
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(underlining above is mine to answer your hypothesis that evolutionists have done any experimentation that proves their as-yet unproven theory)
Is it that the bacteria became resistant or there was bacteria that was already resistant and is now more prevalent? Just like humans and certain diseases.