I very rarely cull a rat or babies if I suspect myco. I also very rarely inject Baytril. An adult female rat I usually give less than 1cc. Has to be injected under the skin, but not deep in the muscle or it can cause a serious ulcer, not pretty!

Like I said, I just cull out the babies, just to stop the stress and slow death of a weak young rat.
Very rarely does an adult have to be culled.

As for ear infections, I use a piece of baytril tab with peanut butter... usually clears up after two or three treatments.
I like baytril injectible, cause I can use it on a lot of differnet animals, so I always keep it around...Ball pythons come to mind
If I don't have baytril tabs, I use tetracycline for birds...cheap, and you can get it without using your vet... My vet pretty much gives me whatever I need though..