WITHDRAWN: How antimicrobial heteroresistance promotes bacterial adaptation to antimicrobial therapy – or not

Abstract

Antimicrobial heteroresistance describes the phenomenon of antimicrobial resistance in only a subpopulation of a bacterial culture. It is usually believed to represent a selectively advantageous strategy promoting bacterial adaptation. Heteroresistance is common in human pathogens, yet often missed during diagnosis, potentially leading to treatment failures. To date, the exact characteristics and evolutionary benefits of heteroresistance are unexplored for most pathogens, including the high-risk pathogenPseudomonas aeruginosa. Here, we systematically studied heteroresistance for a representativeP. aeruginosastrain panel, including genomically distinct clinical and non-clinical isolates. We combined heteroresistance tests, over 2,500 evolution experiments, whole genome sequencing, and mathematical modelling and discovered: (i) an unexpected diversity of heteroresistance profiles across the strain panel, (ii) a high prevalence of beta-lactam, especially carbapenem heteroresistance, (iii) a clear fitness benefit of heteroresistance in treatments with continuously high antimicrobial concentrations, but (iv) no evolutionary advantages of heteroresistance in alternative regimens with initially below-MIC drug doses. We further demonstrate that fast switches between antimicrobials (i.e., fast sequential therapy) can constrain heteroresistance-promoted adaptation. We conclude that heteroresistance is not universally beneficial but only provides an evolutionary advantage under specific conditions, thereby pointing to treatment strategies that remain effective in the face of phenotypic resistance variation.