Introduction Azole resistance in Aspergillus fumigatus is an emerging global concern, significantly limiting treatment options for aspergillosis. The present study aimed to investigate azole resistance mechanisms, focusing on non- cyp51A mutations and efflux pump genes overexpression in environmental isolates of A. fumigatus . Methods A total of 156 soil samples collected from 13 states across India were screened for azole-resistant A. fumigatus isolates. Antifungal susceptibility testing was performed against itraconazole, voriconazole, and posaconazole. Molecular characterization included sequencing of the cyp51A and hmg1 genes. Quantitative real-time PCR (qRT-PCR) was conducted to evaluate the expression levels of cyp51A , hmg1 , and efflux pump genes ( mdr1, mdr4, mfsC, and cdr1B ). Results Nine azole-resistant A. fumigatus isolates were identified. Most resistant isolates exhibited cross-resistance to ITC, VRC, and POS. The cyp51A gene sequencing revealed known mutations, TR46/T289A, alongside novel mutations, including L77W, L477I, A189P, and W223G. Additionally, 18 non-synonymous mutations were discovered in the hmg1 gene, of which 14 were located outside the sterol-sensing domain of Hmg1. In contrast, four mutations (F399V, T410P, G385D, and F362Y) were detected within the SSD region, suggesting its potential role in azole resistance. Furthermore, qRT-PCR analysis revealed upregulation of the cyp51A gene in all resistant isolates, with selective upregulation of efflux pump genes ( mdr1, mdr4, mfsC , and cdr1B ) in various isolates, indicating their probable contribution to resistance. Conclusion Our findings highlight the complexity of azole resistance mechanisms, suggesting that non- cyp51A mutations and efflux pump overexpression are potentially associated with resistance phenotypes. This study emphasizes the need for further functional validation of these resistance mechanisms and novel therapeutic strategies against azole-resistant A. fumigatus .
Sen et al. (Thu,) studied this question.