Decoupling virulence from growth: a synthetic α-helical peptide suppresses Salmonella Typhimurium SPI-1 at sub-inhibitory concentrations

Résumé fourni par la source

ABSTRACT Cationic antimicrobial peptides (CAMPs) can alter bacterial physiology at concentrations below those required to inhibit growth, including modulation of virulence gene expression. In Salmonella Typhimurium, polymyxin B activates the PhoPQ envelope stress response and represses invasion-associated SPI-1 genes such as prgH , but whether synthetic CAMPs can selectively modulate virulence independently of antimicrobial activity remains unclear. Here, we evaluated a panel of rationally designed CAMPs, originally developed against Escherichia coli , for activity against Salmonella Typhimurium under physiological salt conditions used for in vitro induction of SPI-1. Among the peptides tested, the Leu/Ile-rich peptide L1L displayed the greatest antibacterial activity. In a real-time fluorescent assay, L1L also potently repressed prgH promoter activity at a concentration that had no measurable impact on growth kinetics, viability, or ultrastructure. Repression of prgH was accompanied by diminished invasion of epithelial cells in vitro . Relative to polymyxin B, L1L suppressed prgH expression at a smaller fraction of its MIC. Proteomic analysis revealed a coordinated response characterized by increased abundance of PhoPQ-associated CAMP resistance proteins, together with reduced abundance of SPI-1 regulators, structural proteins, effectors, motility proteins, and chemotaxis proteins. In contrast, the corresponding D-enantiomer produced a substantially weaker proteomic response, indicating that stereochemistry influences virulence modulation independently of antibacterial potency. These findings demonstrate that synthetic CAMPs can selectively reprogram Salmonella virulence at sub-inhibitory concentrations and identify L1L as a potent anti-virulence peptide that decouples suppression of host cell invasion from bacterial growth inhibition. IMPORTANCE Synthetic CAMPs offer major advantages over naturally occurring host-defense peptides because their sequence, structure, and physiochemical properties can be rationally engineered. Most design efforts have focused on improving antimicrobial potency, stability, and host compatibility, whereas their ability to modulate bacterial virulence has received much less attention. We show that a simple synthetic α-helical peptide can selectively repress genes required for host cell invasion by Salmonella Typhimurium at concentrations that do not affect bacterial viability or morphology, demonstrating that virulence modulation can be uncoupled from bacterial killing. Because this activity is stereochemically dependent, synthetic CAMPs provide a tractable platform for dissecting how bacteria sense host CAMPs and how these signals are transduced into changes in virulence gene expression. Rational optimization of synthetic CAMPs could therefore both advance our understanding of host-pathogen interactions and facilitate the development of virulence-targeting therapeutics.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.