If my snake were showing symptoms of RI, I would bring to a good vet, one that will do a culture. RI's can be viral or bacterial (or fungal or parasitic, but less likely) and there's no way to know for sure except to culture. You don't want to start a treatment/antibiotic without knowing the kind of infection, since it can potentially do more harm than good.
I wouldn't go to a vet that wants to prescribe antibiotics without doing a culture.