Bumblefoot is a staph infection, and those can't be treated with
tetracycline medications. Penicillin and amoxicillin are optimal
medicines for treating those.
There are additional suggestions for treating bumblefoot on the
Poultry Podiatry page at PoultryPedia.com.
There is also a Chicken Medicine Chart on the website, for
searching for medicines that may be helpful for some chicken
diseases and other problems.