Sensitisation of an Azole-Resistant Aspergillus fumigatus Strain containing the Cyp51A-Related Mutation by Deleting the SrbA Gene.

Daisuke Hagiwara,Katsuhiko Kamei,Akira Watanabe

doi:10.1038/srep38833

Abstract

Azoles are widely used for controlling fungal growth in both agricultural and medical settings. The target protein of azoles is CYP51, a lanosterol 14-α-demethylase involved in the biosynthesis of ergosterol. Recently, a novel azole resistance mechanism has arisen in pathogenic fungal species Aspergillus fumigatus. Resistant strains contain a 34-bp or 46-bp tandem repeat (TR) in the promoter of cyp51A, and have disseminated globally in a short period of time. In this study, we investigated whether an azole-resistant strain with a 46-bp TR (TR46/Y121F/T289A) could be sensitised to azoles by deletion of srbA, encoding a direct regulator of cyp51A. The loss of SrbA did not affect colony growth or conidia production, but decreased expression of cyp51A. The srbA deletion strain showed hyper-susceptibility to medical azoles as well as azole fungicides, while its sensitivity to non-azole fungicides was unchanged. This is the first demonstration that deletion of a regulator of cyp51A can sensitise an azole-resistant A. fumigatus strain. This finding may assist in the development of new drugs to help combat life-threatening azole-resistant fungal pathogens.

Highlights

Filamentous fungi are ubiquitous in nature, and as well as causing significant crop damage, they can be pathogenic for humans
A srbA deletion mutant was successfully constructed in azole-susceptible A. fumigatus strain Af293, and was used as a control throughout the study
Some azole fungicides can inhibit human pathogens such as A. fumigatus[23]; only a few azoles are approved for use in the treatment of aspergillosis

Summary

Introduction

Filamentous fungi (moulds) are ubiquitous in nature, and as well as causing significant crop damage, they can be pathogenic for humans. Similar tandem repeats and insertions in the promoter region of cyp[51] have been reported in several plant pathogens, including Penicillium digitatum[18], Venturia inaequalis[19], Mycosphaerella graminicola[20] and Monilinia fructicola[21]. Some of these mutations have been associated with overexpression of cyp[51]. These studies have shown that constitutive upregulation of cyp51A expression in strains with the tandem repeat or insertion seems to be a prerequisite for the azole resistance. Sensitisation of A. fumigatus strains harbouring the widespread resistance mechanisms would have significant implications for the effective control of human and plant fungal pathogens

Methods

Results

Conclusion