Genetic analysis of common triazole resistance mechanisms in a collection of Aspergillus lentulus clinical isolates from the United States.

Aspergillus fumigatus continues to be the leading cause of invasive aspergillosis. However, the number of cases by drug-resistant cryptic species has increased in recent years. Aspergillus lentulus is a sibling species of Aspergillus section Fumigati that can only be distinguished from A. fumigatus by molecular methods. The clinical importance of this species resides in its low susceptibility to triazoles and intrinsic resistance to amphotericin B, making invasive aspergillosis treatments extremely challenging and producing high mortality rates. In this study, we investigate known molecular mechanisms important for triazole resistance in A. fumigatus in a collection of 25 clinical A. lentulus isolates from the United States. Using CRISPR-Cas9 gene editing technology, we performed cyp51A and hmg1 allele replacements between susceptible and resistant isolates. Phenotypic characterization of the resulting mutants, together with mRNA expression analyzes of cyp51A, cyp51B, and the putative ABC efflux pump, abcC, suggests that triazole resistance in our A. lentulus isolates is independent of the mechanisms studied.