A recombinant lysogenic bacteriophage inhibits <i>Salmonella</i> virulence

The gut environment includes an abundance of chemicals emanating from the host and the microbiota. To colonize animals, <i>Salmonella</i> uses gut chemicals as locational cues to ensure expression of energy-intensive virulence factors only when their production is necessary. <i>cis</i>-2-hexadecenoic acid (c2HDA), a member of the diffusible signal factor family of quorum-sensing signals, potently represses virulence-gene expression by <i>Salmonella</i>. Here, we report the construction and use of a recombinant bacteriophage that can establish lysogeny within <i>Salmonella</i> 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 <i>sieB-esc</i> region and caused it to produce c2HDA by introduction of <i>rpfF</i> of <i>Cronobacter turicensis</i>, encoding the dehydratase/thioesterase required for c2HDA synthesis. We found that <i>Salmonella</i> harboring the lysogenic phage carrying <i>rpfF</i> produced c2HDA and repressed invasion-gene expression both endogenously and exogenously through secretion into the surrounding medium. Consequently, this phage reduced <i>Salmonella</i> invasion of epithelial cells by over 100-fold. We further found that both wild-type and c2HDA-producing phage administered orally to mice reduced <i>Salmonella</i> colonization of the gut, but that the phage carrying <i>rpfF</i> 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 <i>Salmonella</i> colonization of the gut.