Bacterial strains used in this study.

<div><p>Multiple peptide resistance factor (MprF) confers resistance to cationic antimicrobial peptides (AMPs) in several pathogens, thereby enabling evasion of the host immune response. The role of MprF in commensals remains, however, uncharacterized. To close this knowledge gap, we used a common gut commensal of animals, <i>Lactiplantibacillus plantarum</i>, and its natural host, the fruit fly <i>Drosophila melanogaster</i>, as an experimental model to investigate the role of MprF in commensal-host interactions. The <i>L</i>. <i>plantarum ΔmprF</i> mutant that we generated exhibited deficiency in the synthesis of lysyl-phosphatidylglycerol (Lys-PG), resulting in increased negative cell surface charge and increased susceptibility to AMPs. Susceptibility to AMPs had no effect on <i>ΔmprF</i> mutant’s ability to colonize guts of uninfected flies. However, we observed significantly reduced abundance of the <i>ΔmprF</i> mutant after infection-induced inflammation in the guts of wild-type flies but not flies lacking AMPs. Additionally, we found that the <i>ΔmprF</i> mutant compared to wild-type <i>L</i>. <i>plantarum</i> induces a stronger intestinal immune response in flies due to the increased release of immunostimulatory peptidoglycan fragments, indicating an important role of MprF in promoting host tolerance to commensals. Our further analysis suggests that MprF-mediated lipoteichoic acid modifications are involved in host immunomodulation. Overall, our results demonstrate that MprF, besides its well-characterized role in pathogen immune evasion and virulence, is also an important commensal resilience factor.</p></div>