I'm sorry to hear your snake isn't getting better.
I'm pretty sure the culture did not say that oral baytril is best, just that baytril is. Snakes generally do better with injected meds because of their slow metabolism, so I would ask your vet about getting injectable baytril.
If you have not listened to this already, this reptile radio episode with Dr. Stahl has some great info about treating RIs. It takes a while to listen to it, and the RI stuff comes inbetween some other things he talks about, but it is really worthwhile:
http://www.blogtalkradio.com/reptile...ile-veterinary
Perhaps the problem is that your snake has developed a secondary infection, and needs some of that medicine for anaerobic bacteria that Dr. Stahl mentions?