As someone who worked in a veterinary diagnostic lab...I'm so confused as to why this vet would have run a culture...and then prescribe you a dewormer for a bacterial infection. The culture gives them a list of medications that the bacteria is sensitive to.
Unless the ceftazidime injections are what the culture turned up? in that case stopping the injections may have just made the bacteria stronger against it.
At the very least, I would keep your snake in a clean tub with paper towels. Do a small iodine or clorhex soak to flush out the sores and apply a fresh thin layer of silver sulfa or another of the antibiotic creams until you can get another vet and some sort of systemic going.
You may need to do another culture at this point because the resistances may have changed over the 2 months if there isn't any improvement.