If he is in VERY bad condition, as you say, just take him in. Let the Vet see him and then make the decision.

Waiting on the culture is not going to do you any good if the snake dies before its done.. You can always start treatment with a broad spectrum antibiotic now, and then adjust the treatment as needed once the culture comes back.

Of course the stress is also a concern, but at this point, it seems rather critical to do something..

In the end, you will have to make that decision. You are there, you see your snake, go with with you feeling on this one.

I can only tell you what "I" would do in that situation, and there is no guarantee that its the right or wrong thing to do ..

I'm crossing my fingers and toes for you and your poor baby..