Baytril is actually a relatively broad spectrum antibiotic, so a culture isn't absolutely required. It also has an extremely rapid onset of activity, something like 20 to 30 min after administration. As for nebulizing it, there shouldn't be a problem. Just about anything that can be injected can also be delivered by inhalation. With a respiratory infection, inhalation is very likely t be more effective than injection. Also, inhalation presents a MUCH lower risk of systemic side effects than injection. I think the only problem you're going to have is with the delivery. I've never actually tried to get a snake to wear an aerosol mask or use a mouthpiece, but I imagine it would be pretty entertaining to watch. Instead, you're going to want to place the snake in a tub that doesn't have a ton of ventilation and fog the tub. Think gas chamber.

With regard to drug resistant organisms and growth cultures, Simply doing a culture is only half the battle. If you're dealing with a resistant organism, doing a culture is going to tell you that you have an infection caused by an organism that is normally susceptible to Baytril. You still have to figure out what's going to kill it. Ordinarily, a vet will just prescribe a different broad spectrum antibiotic.