Journal Article

Low levels of the second messenger c-di-GMP enhance tolerance and resistance to meropenem in Pseudomonas aeruginosa

Ferrara, Silvia, Labrini, Edoardo, Bertoni, Giovanni, Brignoli, Tarcisio

2026

Overview

The carbapenem antibiotic meropenem is often used to treat life-threatening infections caused by . Previous studies have shown that the susceptibility of to carbapenems is differentially regulated by the RNA chaperone Hfq, depending on the availability of preferred or less preferred carbon sources, a mechanism known as carbon catabolite repression (CCR). In this regulation, Hfq plays a CCR-conditioned repressive role on outer membrane porins that act as entry ports for carbapenems. In this study, we investigated whether meropenem response is modulated by the second messenger c-di-GMP, which is known to regulate several bacterial functions. We used strains with high or low c-di-GMP levels and their Hfq-deficient derivatives to assess the role of c-di-GMP in modulating meropenem susceptibility and tolerance. We show that low intracellular c-di-GMP levels increase meropenem resistance and tolerance at sub-inhibitory concentrations, whereas high c-di-GMP diminishes both traits. Importantly, c-di-GMP status shapes the entire response trajectory, from exponential growth to the stationary phase. Furthermore, we show that c-di-GMP modulates meropenem response through mechanism(s) independent of Hfq-mediated porin repression and exerts a dominant effect over CCR-driven regulation. This study supports the notion that meropenem susceptibility and tolerance are modulated by intracellular c-di-GMP concentrations, with low c-di-GMP levels promoting higher fitness. Our findings indicate that c-di-GMP exerts its regulatory effect through mechanisms distinct from Hfq-mediated porin control, underscoring the existence of parallel regulatory pathways that shape antibiotic response.

• Publisher: Frontiers Media SA,Frontiers Media S.A
• Subject: Anti-Bacterial Agents - pharmacology / antibiotic resistance / antibiotic tolerance / Antibiotics / Biofilms / c-di-GMP / Carbapenems / Carbon / carbon catabolite repression / Carbon sources / Catabolite Repression / Cloning / Cyclic GMP - analogs & derivatives / Cyclic GMP - metabolism / Drug Resistance, Bacterial / E coli / Extracellular matrix / Gene Expression Regulation, Bacterial / Genes / Hfq / Host Factor 1 Protein - genetics / Host Factor 1 Protein - metabolism / Intracellular / Meropenem / Meropenem - pharmacology / Metabolism / Microbial Sensitivity Tests / Original Research / Physiology / Plasmids / Porins / Porins - metabolism / Proteins / Pseudomonas aeruginosa / Pseudomonas aeruginosa - drug effects / Pseudomonas aeruginosa - genetics / Pseudomonas aeruginosa - metabolism / Second Messenger Systems / Stationary phase / Statistical analysis / Thienamycins - pharmacology