Vultures feed on carrion at stages of decay that other vertebrates avoid. Stomach pH in Gyps vultures is reported to be around one or lower, acidic enough to destroy most bacteria and their spores before they reach the intestine, along with the toxins many produce.
Genomic surveys of vulture gut communities have found the surviving flora dominated by groups including Clostridia and Fusobacteria, taxa associated with decomposition and, in other animals, with disease. The vultures appear to tolerate them, and this filtering role is why vulture populations are described as reducing the circulation of carcass-borne pathogens in a landscape.
The important caveat is that chemical resilience does not confer general immunity. The collapse of South Asian Gyps vultures from the late 1990s, exceeding ninety per cent in some populations, was caused by the veterinary drug diclofenac in cattle carcasses, which causes kidney failure in vultures. The gut that neutralises anthrax spores offers no protection against a pharmaceutical residue.