ICP1 bacteriophage treatment antagonizes colonization of the zebrafish larval intestine by Vibrio cholerae

Outbreaks of cholera pose a major threat to human health. Currently, antibiotics are the most effective treatment against the causative agent, the bacterium Vibrio cholerae. However, the use of antibiotics eventually leads to the emergence of resistant strains, which necessitates the need for alternative approaches. The use of bacteriophages to target the infection by antibiotic-resistant bacteria is one promising alternative. While clearance of Vibrio cholerae with the use of phages has been performed on several animal models, none of these models are naturalistic hosts of V. cholerae. Therefore, we set out to investigate the interaction between V. cholerae and bacteriophage ICP1 both in vitro and in vivo in a naturalistic host, the zebrafish model, Danio rerio. To study the interplay between host, bacteria, and phages, we used a combination of light and ultrastructural imaging techniques, including confocal fluorescence microscopy, serial block face scanning electron microscopy (EM) imaging, and cryogenic EM, which allowed us to investigate both the colonization process by V. cholerae and clearance by the ICP1 bacteriophage. In addition, we determined the effects of the microbiome on this treatment by using germ-free, conventionalized, and monoassociated zebrafish larvae as a host. Independent of the presence and composition of microbiomes used here, V. cholerae efficiently colonized the larval intestine. Finally, we demonstrate significant in vivo clearance of V. cholerae N16961-dsRED by ICP1, underscoring the role of phage-bacteria dynamics in shaping pathogen colonization within the zebrafish larval host.