Identification of Pseudomonas aeruginosa virulence factors in a Drosophila melanogaster intestinal infection model. Samantha Haller, Ferrandon Dominique. UPR9022 , CNRS, Université de Strasbourg, IBMC, Strasbourg, France.

   Pseudomonas aeruginosa is an opportunistic pathogen able to infect plants, Drosophila melanogaster and humans. P. aeruginosa is the third most common pathogen at the origin of nosocomial infection and is multi-resistant against antibiotics. Therefore, there is a need to find novel therapeutic targets. Although P. aeruginosa pathogenicity has been extensively studied, mostly in vitro, the interactions between the Drosophila immune response of the host, especially the cellular immune response, and P. aeruginosa remain poorly understood.
   Previously, we have shown that some orally ingested P. aeruginosa (PA14) bacteria escape the intestinal barrier and proliferate in the hemolymph until the flies succumb to systemic infection, i.e., bacteremia (Limmer et al., 2011). Moreover, we found that the quorum sensing transcription factor RhlR plays a key role in circumventing the cellular immune response against PA14. The same intestinal infection model was used to identify important virulence factors of PA14 and genes potentially mediating rhlRs phenotype. We have screened in wild-type Drosophila 348 mutants PA14 that displayed an attenuated virulence in an intestinal infection model in C. elegans (Feinbaum et al., 2012). 20 PA14 mutants exhibited a reproducible attenuated virulence phenotype. Among these bacterial mutants, we found mutants for genes implicated in peptidoglycan remodeling, transcription and regulation of gene transcription, type two secretion system, exotoxins, metabolism, and some known virulence factors. Five of these bacterial mutants behave like rhlR mutants in phagocytosis-blocked Drosophila, that is, they recover full virulence. Thus they represent candidates for genes that are regulated by RhlR. Unexpectedly, we discovered that RhlR's function in circumventing the cellular immune response is likely independent from its role in quorum sensing (perception of the concentration of a C4-homoserine lactone), a situation never described before.