A recombinant lysogenic bacteriophage inhibits Salmonella virulence

The gut environment includes an abundance of chemicals emanating from the host and the microbiota. To colonize animals, Salmonella uses gut chemicals as locational cues to ensure expression of energy-intensive virulence factors only when their production is necessary. cis-2-hexadecenoic acid (c2HDA), a member of the diffusible signal factor family of quorum-sensing signals, potently represses virulence-gene expression by Salmonella. Here, we report the construction and use of a recombinant bacteriophage that can establish lysogeny within Salmonella and induce it to produce c2HDA, thus repressing functions essential to its own virulence. We engineered the temperate phage P22 to favor lysogeny through transposon mutagenesis of the sieB-esc region and caused it to produce c2HDA by introduction of rpfF of Cronobacter turicensis, encoding the dehydratase/thioesterase required for c2HDA synthesis. We found that Salmonella harboring the lysogenic phage carrying rpfF produced c2HDA and repressed invasion-gene expression both endogenously and exogenously through secretion into the surrounding medium. Consequently, this phage reduced Salmonella invasion of epithelial cells by over 100-fold. We further found that both wild-type and c2HDA-producing phage administered orally to mice reduced Salmonella colonization of the gut, but that the phage carrying rpfF reduced gut inflammation more than did the phage without this gene. Collectively, our data show that a recombinant phage can be used as the vehicle for cytoplasmic delivery of c2HDA, thus providing a targeted means to manipulate Salmonella colonization of the gut.