Investigation of voriconazole heteroresistance in clinical isolates of from a multicenter study in China.

Heteroresistance refers to the presence of subpopulations within seemingly homogeneous microbial cells that exhibit varying sensitivities to antifungal agents, potentially contributing to treatment failure. Our study investigated the heteroresistance levels of clinical isolates of collected from a multicenter study in China. A total of 62 isolates from 31 research centers, representing five different genotypes, were analyzed. We assessed the minimal inhibitory concentrations (MICs) of voriconazole (VRC), the level of heteroresistance to voriconazole (LHV), the strains' capacity for adaptation to high VRC concentrations (ADP), and the stability of the heteroresistance phenomenon. The isolates had low VRC MICs (average 0.038 µg/mL), with 95.2% (59/62) classified as wild type. Heteroresistance to VRC was observed in all isolates, with an average LHV (0.25-4 µg/mL) 23 times higher than the MICs (0.012-0.19 µg/mL). Additionally, 90.3% of strains tolerated VRC concentrations at least 16 times the MICs, with heteroresistant subpopulations appearing at frequencies ranging from 0.002% to 0.830%. Furthermore, the strains rapidly adapted to elevated drug concentrations following brief exposure to VRC, with 71.0% tolerating VRC at 8 µg/mL and an average ADP value 285 times the MICs. However, the strains gradually lost this resistance when serially passaged on drug-free SDA plates, with the time required for resistance loss varying among strains. Our study is the first to reveal the presence of heteroresistance in clinical , adding to the body of research on fungal heteroresistance and posing challenges to the clinical interpretation of MIC values for guiding treatment.IMPORTANCE has become an increasingly important fungal pathogen responsible for invasive infections in clinical settings. Due to its natural resistance to flucytosine and echinocandin classes, azole drugs, especially voriconazole, are the mainstay of treatment. The phenomenon of heteroresistance may be associated with treatment failure in fungal infections; however, this phenomenon remains unclear in . Our study provides the first comprehensive characterization of voriconazole heteroresistance in significantly advancing our understanding of antifungal resistance dynamics in this emerging pathogen. Our findings also challenge the reliability of conventional minimal inhibitory concentration-based therapeutic guidance for infections.