Vibrio cholerae is an aquatic bacterium that is the aetiologic agent of the acute diarrhoeal disease cholera, which is endemic in many countries. In aquatic environments, V. cholerae interacts with a wide variety of organisms, including heterotrophic protists (protozoa). Several species of these bacterial predators have been reported to release live, undigested bacteria in expelled food vacuoles (EFVs) when feeding on certain pathogens. While the production of EFVs has been reported, their biological role as a vector for the transmission of pathogens remains unknown.
Using co-incubation assays, we report that Tetrahymena pyriformis releases large numbers of EFVs when feeding on V. cholerae. The EFVs are stable, the bacterial cells within are protected from multiple stresses (low pH, antimicrobials and starvation) and vast numbers quickly escape when incubated at 37°C or in the presence of nutrients. We show that OmpU, a major outer membrane protein positively regulated by ToxR, plays a significant role in the production of EFVs. Importantly, cells released from EFVs have growth and colonisation advantages over planktonic cells both in vitro and in vivo and are highly infectious (as shown in the infant mouse model of infection). Our results suggest that EFVs facilitate V. cholerae survival in environment and in the gastric environment, enhancing infectious potential and may significantly contribute to the dissemination of epidemic V. cholerae strains. These results establish a new understanding of the mechanisms of persistence and the modes of transmission of V. cholerae and may further apply to other opportunistic pathogens that have been shown to be released by protists in EFVs. Results presented here will improve the identification and tracking of pathogens in the environment.