Molecular mechanisms of cross-resistance to azole antifungal agents in a clinical isolate of Aspergillus fumigatus: a preliminary study

Abstract

Objective To investigate the molecular mechanisms of cross-resistance to azoles in a clinical isolate of Aspergillus fumigatus. Methods A. fumigatus was isolated from a patient with invasive aspergillosis.Clinical Laboratory Standard Institute M38-A2 broth microdilution method and E-test method were used to determine the minimum inhibitory concentrations (MICs) or minimum effective concentration (MEC) of itraconazole, voriconazole, amphotericin B, posaconazole and caspofungin for the A. fumigatus isolate. DNA was extracted from the isolate and subjected to the amplification of cyp51A gene encoding the target enzyme of azole antifungal agents followed by sequence analysis. Results The broth microdilution test showed that the MEC of caspofungin was 0.5 mg/L, and MICs of itraconazole, voriconazole and amphotericin B were ≥ 16 mg/L,8 mg/L and 1 mg/L, respectively, for this isolate; while E-test assay revealed that the MICs of caspofungin,itraconazole, voriconazole, amphotericin B and posaconazole were 0.047 mg/L, ≥32 mg/L,≥32 mg/L, 12 mg/L and ≥32 mg/L, respectively. Sequence analysis showed an insertion of a 34-bp tandem sequence in the promoter region of the cyp51A gene as well as a T364A point mutation causing the substitution of leucine 98 (L98H). In addition, there were some other mutations in the cyp51A gene of this isolate, such as A137T,G585A, C814A, G836C, T991C and A1350G, which could result in corresponding amino acid substitutions.Conclusions An A. fumigatus strain with cross-resistance to azole antifungal agents is isolated. There is an insertion of a 34-bp tandem sequence into the promoter region as well as a T364A point mutation in the cyp51A gene, which contribute to the cross resistance to azole antifungal agents including itraconazole, voriconazole,and posaconazole. In addition, other mutations causing amino acid substitutions have also been detected in the cyp51 A gene of this isolate. Key words: Aspergillus fumigatus; Azoles; Drug resistance, multiple, fungal; cyp51A