Reversing olorofim activity reveals multifactorial drug tolerance inAspergillus fumigatus

Abstract

AbstractDrug tolerance leads to increased cell survival upon antimicrobial treatment and its contribution to the emergence of antimicrobial resistance is well described in bacteria. However, this antimicrobial response is still overlooked in human fungal pathogens, such asAspergillus fumigatus. Due to the global increase of antifungal resistance to currently used antifungals to treat aspergillosis, new antifungals such as the pyrimidine synthesis inhibitor olorofim have been developed. Here, we show that reversing olorofim activity by the addition of exogenous pyrimidines reveals the presence of olorofim tolerance in 4% ofA. fumigatusenvironmental strains. Disrupting cell wall integrity or inhibiting efflux transport in those strains reverses olorofim tolerance, yet inconsistently, thus suggesting that this response may have a multifactorial origin. Understanding the mechanistic basis ofA. fumigatustolerance to olorofim will increase our knowledge on its contribution to resistance allowing the development of strategies to suppress it before this promising antifungal reaches clinical implementation.