more than two dozen microwaves located in homes, offices, and even in chemistry labs.
Every lab I’ve ever been in has a had a big sign on the fridge saying “Don’t store experiments in this fridge” (often with profanity), so I’d expect the microwave in a chemistry lab to be more filthy than the average home. Plus, this bunch of microbiologists chose to test the microwave in a chemistry lab, rather than the one in their own department, which says a lot about what they found in their own microwave…
(PS, the link to the actual study is broken)