First you test for it.....NEVER TREAT WITH ANTIBIOTICS AS A PRECAUTION.....that is how microbes develop immunity....you needlessly treat now and if foul brood does get a foothold later when the antibiotic is present the bacteria can change its drug receptors and tada....you started a resistant strain of foulbrood. Right now we have a MRSA (methicillin resistant staphlycoccus aureus) staph infection outbreak in kentucky......Does not effect our bees, but it does our kids and is really hard to treat..... These resistance come from over use/unnessicary use of antibiotics.
Good Judgement comes from Experience. Experience comes from Poor Judgement.