Here is a little info on TM resistant AFB from Canada:

1.  Destroy all colonies exhibiting symptoms of OTC resistant AFB when they
first appear. Removing only diseased comb and medicating will not be
effective and will risk the possible spread of resistance.

2. If a significant number of colonies have been infected (>1% of colonies),
medicate the remaining healthy colonies with a veterinary prescribed
antibiotic, such as Tylan. Tylan should only be applied to colonies located
within 2 km of where infected colonies were located. Presently, Tylan can
only be prescribed following positive identification of OTC-resistance by
the provincial apiarist.

http://www.capabees.ca/rafb.htm

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