when i have my colonies tested, i cut a section of the comb that contains sealed brood. ideally the brood is still in the soft larval stage not almost fully formed into pupa. then i capture about 30 live bees and send them along to be tested.
the contents of the adult bee gut are smeared and examined under a microscope. since it's the university that does the tests, i was fortunate to be able to examine the slide since they used a teaching microscope with a pointer. my slides didn't have any signs of AFB spores, but i was shown a slide that did have the spores. the spores look rod-like and slightly elongated. the microbiologist explained to me that there is a type of spore which looks very similar and they call it the lactic type. thats the good kind of bacteria.
it's not only the presence of the spores they look at, but also the number and movement. once they see suspicious spores, they start making a culture test and that takes some time because they have to grow it in a medium. the culture test is the most definite and unarguable and thats when you start praying while waiting for the results LOL.
best info so far, thank you very much tig!