Overexpression of Efflux Pump Genes is an Alternative Mechanism in Voriconazole Resistant Aspergillus fumigatus isolates Without Relative Mutations in CYP5A

Background: The overexpression of the efflux transporter genes is one of the important mechanisms of resistance in fungal pathogens such as Candida and Aspergillus species. Objective: Here, the expression alterations of drug efflux transporter genes were evaluated in non- Cyp51A voriconazole-resistant Aspergillus fumigatus isolates. Methods: Six A. fumigatus isolates including four voriconazole-resistant isolates with and without azole-resistance-related mutations in addition to two susceptible A. fumigatus isolates were selected from 300 previously characterized A. fumigatus clinical and environmental isolates, received during 2013-2015. In order to extract RNA, the minimum inhibitory concentrations (MICs) for the isolates were determined according to the broth microdilution protocol regarding the Clinical and Laboratory Standards Institute document M38-A2 (CLSI, 2008). Alteration in the expression of AfuMDR1, AfuMDR2, AfuMDR3, AfuMDR4, Cyp51A, and atrF was studied using the real-time polymerase chain reaction assay. Results: Based on REST® output, significant overexpression of atrF, AfuMDR1, AfuMDR3, and AfuMDR4/Cyp51A, atrF, AfuMDR2, AfuMDR4 genes was observed in the isolates without azoleresistance- related mutations, respectively. No significant overexpression was seen in the isolates with T34/L98H except for the AfuMDR3 and AfuMDR4(P< 0.05). Conclusion: Our results support the hypothesis that efflux pump transporters can contribute to voriconazole resistance in A. fumigatus.