Dogs, ear infections...

Im no vet nor will I tell you I know more than your Vet but having over 80 Bulldogs (what mainstream news call "pit bulls") on my yard. Having dogs since 1979 I can say I qualify as a experienced dog owner.
There are many mitigating factors when it comes to a dogs health, from diet (rarer than most other reasons on average) to hygiene to plain bad luck.
What I think you should do is eliminate all the rhetoric and pay attention to what your dog does, goes, eats and take it from there.
Do the ears smell ? Bad smell ? Sweet like smell ? Is he continuously scratching at them, rubbing his ears against anything, floor, walls, chairs (furniture) it could a mite issue and not a bacteria type of infection.
You would be surprised what a little coconut oil can do for your dogs ears, Apple Cider (vinegar)
In fact cod liver oil is great for their skin (hair) so lie I said they're are dozen reasons what could be wrong make sure to eliminate one at a time before you go Dr.Doolittle on the poor boy.
Just my thoughts on the matter...
MAPS