Andy Camilli, Tufts University

Preventing Cholera Using Bacteriophages

The biological factors that govern the dissemination and transmission of toxigenic Vibrio cholerae remain ill defined. By studying hundreds of cholera patient rice-water stools from clinics in Bangladesh and Haiti we found that most cholera patients shed high titers of at least one of three distinct species of V. cholerae-specific virulent (lytic) bacteriophage. We provide evidence that these phages prey extensively on V. cholerae within the human gastrointestinal tract, thus impacting the infection, dissemination, transmission and evolution of V. cholerae. Using genetic and phenotypic analyses we have begun to reveal the biology of these phages and important details of the ongoing arms race between each phage and V. cholerae. We have shown that the LPS O1 antigen and OmpU serve as receptors for these phages. V. cholerae phage-resistant escape mutants arise from mutations in the genes required for the production of these receptors, resulting in strains that are avirulent. By combining these phages we have developed a cocktail that, when administered to animals up to 24 hours prior to challenge, can prevent cholera. The combination of phages appears to prevent the appearance of mutants that can escape predation by all three phages. Ongoing studies seek to determine the frequency (or lower bound) at which escape mutants to the phage cocktail arise, as well as the impact, if any, of the phage cocktail on the gut microbiota in healthy animals.