Evolution of Resistant Mutants in Pseudomonas aeruginosa Persister Cells Under Meropenem Treatment

Bacterial persisters are dormant cells that survive antibiotic treatment, serving as a reservoir for the emergence of resistant mutations. The evolution of antibiotic resistance poses a significant challenge to public health. In this study, we investigated the development of resistance in <i>Pseudomonas aeruginosa</i> persister cells by exposing the reference strain PA14 to meropenem and tracked the emergence of resistance mutations over serial passages. Whole-genome sequencing of the populations or individual resistant strains revealed evolutionary trajectories. In the initial passages, low-level meropenem-resistant mutants harbored various mutations, accompanied by increasing population survival. Then, mutations in the <i>oprD</i> gene appeared, followed by mutation in the <i>mexR</i> gene in most of the cells, leading to high-level meropenem resistance and collateral resistance to ciprofloxacin. Our study provides insights into the evolutionary pathways of <i>P. aeruginosa</i> under lethal antibiotic pressure, highlighting the dynamic interplay between persister cells and the emergence of resistance mutations.