The George C. Williams Prize for 2023 for the best article published in Evolution, Medicine, and Public Health in 2022 is awarded to: Evolved resistance to a novel cationic peptide antibiotic requires high mutation supply byt Santos-Lopez, A., Fritz, M. J., Lombardo, J. B., Burr, A. H. P., Heinrich, V. A., Marshall, C. W., & Cooper, V. S. (2022).  Evolution, Medicine, and Public Health10(1), 266–276. https://doi.org/10.1093/emph/eoac022

Joint primary authors Alfonso Santos and Melissa Fritz (pictured) will present the work at the ISEMPH 2023 meeting in August in Irvine, California.

Warmest thanks to the Editor, Cynthia Beall, and the Prize Committee:  Sylvia Cremer (chair), Bridget Alex, and Roderich Römhild and to donors who make the Prize possible.

Abstract

Background and Objectives

A key strategy for resolving the antibiotic resistance crisis is the development of new drugs with antimicrobial properties. The engineered cationic antimicrobial peptide WLBU2 (also known as PLG0206) is a promising broad-spectrum antimicrobial compound that has completed Phase I clinical studies. It has activity against Gram-negative and Gram-positive bacteria including infections associated with biofilm. No definitive mechanisms of resistance to WLBU2 have been identified.

Methodology

Here, we used experimental evolution under different levels of mutation supply and whole genome sequencing (WGS) to detect the genetic pathways and probable mechanisms of resistance to this peptide. We propagated populations of wild-type and hypermutator Pseudomonas aeruginosa in the presence of WLBU2 and performed WGS of evolved populations and clones.

Results

Populations that survived WLBU2 treatment acquired a minimum of two mutations, making the acquisition of resistance more difficult than for most antibiotics, which can be tolerated by mutation of a single target. Major targets of resistance to WLBU2 included the orfN and pmrB genes, previously described to confer resistance to other cationic peptides. More surprisingly, mutations that increase aggregation such as the wsp pathway were also selected despite the ability of WLBU2 to kill cells growing in a biofilm.

Conclusions and implications

The results show how experimental evolution and WGS can identify genetic targets and actions of new antimicrobial compounds and predict pathways to resistance of new antibiotics in clinical practice.