Activity of a Synthetic Peptide Targeting MgtC on Intramacrophage Survival and Biofilm Formation.

Antivirulence strategies aim to target pathogenicity factors while bypassing the pressure on the bacterium to develop resistance. The MgtC membrane protein has been proposed as an attractive target that is involved in the ability of several major bacterial pathogens, including , to survive inside macrophages. In liquid culture, MgtC acts negatively on biofilm formation. However, a putative link between these two functions of MgtC in has not been experimentally addressed. In the present study, we first investigated the contribution of exopolysaccharides (EPS) in the intramacrophage survival defect and biofilm increase of mutant. Within infected macrophages, expression of EPS genes and was increased in a mutant strain comparatively to wild-type strain. However, the intramacrophage survival defect of mutant was not rescued upon introduction of or mutation, suggesting that MgtC intramacrophage role is unrelated to EPS production, whereas the increased biofilm formation of mutant was partially suppressed by introduction of mutation. We aimed to develop an antivirulence strategy targeting MgtC, by taking advantage of a natural antagonistic peptide, MgtR. Heterologous expression of in PAO1 was shown to reduce its ability to survive within macrophages. We investigated for the first time the biological effect of a synthetic MgtR peptide on . Exogenously added synthetic MgtR peptide lowered the intramacrophage survival of wild-type PAO1, thus mimicking the phenotype of an mutant as well as the effect of endogenously produced MgtR peptide. In correlation with this finding, addition of MgtR peptide to bacterial culture strongly reduced MgtC protein level, without reducing bacterial growth or viability, thus differing from classical antimicrobial peptides. On the other hand, the addition of exogenous MgtR peptide did not affect significantly biofilm formation, indicating an action toward EPS-independent phenotype rather than EPS-related phenotype. Cumulatively, our results show an antivirulence action of synthetic MgtR peptide, which may be more potent against acute infection, and provide a proof of concept for further exploitation of anti- strategies.