From the article:
But for the general public, the implications of the study are simpler. “A microwave is not a pure, pristine place,” Porcar says. It’s also not a pathogenic reservoir to be feared, he says. But he does recommend cleaning your kitchen microwave often — just as often as you would scrub your kitchen surfaces to eliminate potential bacteria.
Seems like it’s pretty much like any other surface in your kitchen, it requires regular cleaning.
it’s like any other surface anywhere - even if you clean it regularly it will still have bacteria on it. but the thing is most bacteria are not harmful.