Deciphering meropenem persistence in Acinetobacter baumannii facilitates discovery of anti-persister activity of thymol.

Abstract

Decades of antibiotic misuse have accelerated the emergence of multi- and extensively drug-resistant bacteria. Bacterial pathogens employ several strategies such as antibiotic resistance, tolerance, and biofilm formation in response to extreme environments and antibiotic stress. Another crucial survival mechanism involves the stochastic generation of bacterial subpopulations known as persisters, which can endure high concentrations of antibiotics. Upon removal of antibiotic stress, these subpopulations revert back to their original phenotype which links them to the relapse and recalcitrance of chronic infections, a significant problem in clinical settings. Persistent infections are particularly notable in Acinetobacter baumannii, a top-priority ESKAPE pathogen, where carbapenems serve as last-resort antibiotics. Several reports indicate the rising therapeutic failure of carbapenems due to persistence, underscoring the importance of developing anti-persister therapeutics. In this study, we explored the mechanisms of transient persister formation in A. baumannii against meropenem. Our investigation revealed significant changes in membrane properties and energetics in meropenem persisters of A. baumannii, including a noteworthy increase in tolerance to other antibiotics. This understanding guided the evaluation of an in-house collection of GRAS status compounds for their potential anti-persister activity. The compound thymol demonstrated remarkable inhibitory activity against meropenem persisters of A. baumannii and other ESKAPE pathogens. Further investigation revealed its impact on persister cell physiology, including efflux pump inhibition and disruption of cellular respiration. Given our results, we propose a compelling strategy where thymol could be employed either as a monotherapy or in combination with meropenem in anti-persister therapeutics.