Commensal pathogen competition impacts host viability

Significance Enteric pathogens including the causative agent of cholera, Vibrio cholerae , use the type-six secretion system (T6SS) to kill commensal microbes in the host intestine. Eradicating competing microbes allows pathogens to improve colonization. However, it is not known whether commensal destruction has additional consequences on host viability. We used the Drosophila model of cholera to determine the impacts of T6SS on fly health and longevity. We found that T6SS-dependent competition with the symbiotic Acetobacter pasteurianus intensified disease symptoms, and accelerated host death. Gnotobiotic flies without A. pasteurianus abolished T6SS-dependent death, and reintroduction of A. pasteurianus alone was sufficient to restore accelerated death. These observations implicate T6SS-dependent interactions with commensal bacteria as a factor for the progression of cholera.