Have you tried any home remedies? Have you cleaned and disinfected his tank or tub correctly and consistently? Are you able to quarantine in an effective way? Is your husbandry correct? Also, I didn't see any of your other posts, but did the vet do a culture? Not all RI are bacterial. I'm just getting through fighting an RI in my adopted male and he had Ecoli on top of it all. Since you have a collection I'm assuming you tried everything possible, but if you are considering giving up I would have to agree with KMG that you should rehome the snake. Just be honest about why you are doing so.