I'd start with the rope test (matchstick, twig etc.) and if it ropes I would do a Holts milk test. Short version is make some nonfat dry milk and get it up to body temp (in a testube under your arm works well). Dip the stick in the goo and put it in the testube. If it's AFB the solution will precipitate and become transparent (though maybe slitghly yellow or brown). It will no longer be milky and opaque. if it does not precipitate it is not AFB.
The Hive and The Honey Bee. "Extensively Revised in 1975" edition. Page 623.
"The Holst milk test: The Holst milk test was designed to identify enzymes produced by B. larvae when speculating (Host 1946). A scale or toothpick smear is swirled gently into a tube containing 3-4 milliliters of 1 per cent powdered skim milk and incubated at body temperature. If the spores of B. larvae are present, the cloudy suspension will clear in 10-20 minutes. Scales from EFB or sacbrood are negative in this test."