Fosfomycin Attenuates Virulence of Multidrug-Resistant <i>Pseudomonas aeruginosa</i> by Quorum-Sensing Inhibition and Protects Mice from Acute Lung Injury

Abstract

Background: Multidrug-resistant Pseudomonas aeruginosa (MDR-PA) poses a severe threat, with its pathogenicity heavily reliant on quorum sensing (QS). Fosfomycin (FOM), known for its biofilm penetration and synergy with other antibiotics. Objectives: In this study, the potential of FOM to inhibit QS and its virulence at sub-inhibitory concentrations was investigated. Methods: We determined the sub-MIC of FOM that does not affect bacterial growth. Its impact on virulence phenotypes (biofilm formation, swimming motility, pyocyanin production, protease activity) and QS gene expression (las, rhl, pqs systems) was assessed in vitro. Efficacy was further evaluated in a murine model of MDR-PA pneumonia. Results: Fosfomycin at 1/8 minimum inhibitory concentration (MIC; 0.25 μg/mL) did not alter Pseudomonas aeruginosa (PA) growth but significantly reduced swimming motility (P < 0.001), biofilm biomass (P < 0.001), pyocyanin (P < 0.001), and extracellular protease activity (P < 0.05). Quantitative real-time PCR (qRT-PCR) revealed marked downregulation of lasR (27 %), lasI (17 %), rhlR (54 %), rhlI (48 %), and pqsR (10 %) (all P < 0.01), whereas pqsE was unchanged. In vivo, FOM-treated mice exhibited less weight loss (P < 0.05), 100 % survival versus ~60 % in untreated (P < 0.01), reduced bronchoalveolar lavage fluid (BALF) cytokines (all P < 0.05), and preserved alveolar architecture. Conclusions: Sub-inhibitory FOM blunts Las/Rhl/Pqs QS circuits, modestly but consistently attenuates key virulence phenotypes, and protects against MDR-PA pneumonia. These findings support exploring FOM as a QS-targeting adjuvant in MDR-PA infections.