for what it's worth, the information to medicate packaged bees in feed with antibiotics to act as a preventative for foul brood is floating around. although not practiced by the majority here on beemaster, its not unheard of at websites like baldwinbees.com
I won't use it myself. While not necessary, some thing I haven't tried but will this season before installing packages in their homes is checking for mites with powered sugar. here's one way to do it from baldwinbees.
place a serving tray down on the ground, turn package screen side up on the tray, sprinkle a ¼ to ½ cup of powdered sugar through the screen allowing it to cover the bees. The mites will release and fall through the screen on to the tray along with the powdered sugar. Pour contents from the tray in to a water to see what you find. The sugar will wash off the mites making them appear in the water. If the mite count is high (20 to 35) you may want to treat all your packages for mite using this same method.