A specific innate immune response silences the virulence of Pseudomonas aeruginosa in a latent infection model in the Drosophila melanogaster model

Environmentally ubiquitous bacteria have acquired extensive abilities to adapt to variable environments, bestowing to some of them the potential to become opportunistic pathogens. This may translate into distinct infection modes according to the route of entry. Whereas Pseudomonas aeruginosa is considered to have two major modes of infection, acute by planktonic cells or chronic through the establishment of biofilms, we report here a novel type of infection whereby ingested bacteria escape from the digestive tract and silently colonize tissues as single cells without strongly affecting the lifespan of the Drosophila host. The bacteria appear to be dormant, a feature shared with persister cells that elude the action of antibiotics. They are characterized by distinct bacterial and colony morphologies, cell surface and motility properties. Their virulence program can nevertheless be reactivated spontaneously or upon injury. We also report that an important host defense of invertebrates, melanization, is activated upon escape of the bacteria into the internal milieu. This activation not only promotes the dormancy of the colonizing bacteria but also protects the host to some degree against secondary infections. As P. aeruginosa is a member of the microbiota of a sizable fraction of human populations, these discoveries may become medically relevant.This article has been formally accetpted by Plos Pathogens, the DOI number for it is: 10.1371/journal.ppat.1012252.