Many vet when asked will tell you they will see reptiles yet have no experience I have met a few of them even one that thought a snake about to shed had scale rot here is what I can tell you
Bathing a sick animal is a bad idea, a snake with a RI does not need the additional stress it's completely counter productive, bathing an healthy one is not good either.
Oral anti-bitotics are VERY inefficient with snakes.
Did he perform a culture? What is the cause of the RI? How long is the treatment?