Enhanced Efflux Activity Facilitates Drug Tolerance in Dormant Bacterial Cells

TLDR

Natural gene‑expression variability in isogenic bacterial populations generates phenotypic subgroups, including persisters that display high antibiotic tolerance and are traditionally linked to cell dormancy. We demonstrate that persisters treated with β‑lactams accumulate less drug due to enhanced efflux, especially via TolC, and that combining efflux inhibitors with antibiotics effectively diminishes persister formation.

Abstract

Natural variations in gene expression provide a mechanism for multiple phenotypes to arise in an isogenic bacterial population. In particular, a sub-group termed persisters show high tolerance to antibiotics. Previously, their formation has been attributed to cell dormancy. Here we demonstrate that bacterial persisters, under β-lactam antibiotic treatment, show less cytoplasmic drug accumulation as a result of enhanced efflux activity. Consistently, a number of multi-drug efflux genes, particularly the central component TolC, show higher expression in persisters. Time-lapse imaging and mutagenesis studies further establish a positive correlation between tolC expression and bacterial persistence. The key role of efflux systems, among multiple biological pathways involved in persister formation, indicates that persisters implement a positive defense against antibiotics prior to a passive defense via dormancy. Finally, efflux inhibitors and antibiotics together effectively attenuate persister formation, suggesting a combination strategy to target drug tolerance.