Vibrio vulnificus are pathogenic bacteria commonly found in raw or undercooked seafood. In humans, members of this bacterial species can cause vomiting, diarrhea, and abdominal pain, but how V. vulnificus makes it past the gut’s defenses has remained unclear. To find out, researchers examined fecal samples from mice that died of V. vulnificus infection. These mice showed a notable decrease in the abundance of Bacteroides vulgatus, beneficial gut bacteria that normally help block disease. When cultured together, V. vulnificus led to a decrease in the survival of B. vulgatus. This antagonistic effect was found to be mediated by the compound cFP, secreted by V. vulnificus. Direct treatment with cFP collapsed the cellular structure of B. vulgatus., and mice fed cFP showed significantly lower levels of B. vulgatus and an increased susceptibility to infection by V. vulnificus. These effects were traced to the interaction between cFP and the ObgE protein found in B. vulgatus. Isolating the role of ObgE could help scientists understand how V. vulnificus primes the gut for invasion.