Antifungal Susceptibility and cyp51A Gene Variation Analysis of Aspergillus fumigatus Isolated from Soils in Tea-Growing Areas of Guizhou, China

Aspergillus fumigatus is the predominant pathogenic fungus responsible for aspergillosis. In recent years, the global detection rate of azole-resistant A. fumigatus (ARAF) has continuously increased, and the extensive application of agricultural azole fungicides has been recognized as a crucial driving factor for the emergence and spread of resistance mutations in environmental A. fumigatus. Previous investigations conducted by our research team in karst vegetable fields of Guizhou Province revealed that the resistance rate of local A. fumigatus was only 0.49%, which was markedly lower than those reported in most previous studies in China and outside of China. To supplement the prevalence data of azole resistance across different habitats in this region, a total of 191 environmental A. fumigatus strains were isolated from nine tea plantations across Guizhou. In this study, two clinically prevalent azole drugs, itraconazole and voriconazole, were used for antifungal susceptibility testing, and the triazole target gene cyp51A of all isolates was sequenced and analyzed. Antifungal susceptibility results demonstrated that the MIC ranges of the tea plantation A. fumigatus population were 0.015–0.5 μg/ml for itraconazole and 0.031–0.25 μg/ml for voriconazole, with no evidence of triazole resistance. Genetic analysis identified ten different gene mutations among 29 isolates, all of which were classified as non-resistance-associated mutations. Among these mutations, four were synonymous mutations, including 267G→A, 540G→A, 1074A→G, and 1362T→C, while six were non-synonymous mutations, including 137T→A, 514A→G, 743A→C, 744T→A, 765C→G, and 1279G→A. These non-synonymous mutations resulted in five amino acid substitutions in 25 strains, namely F46Y, M172V, N248T/K, D255E, and E427K. The N248T/K mutation exhibited the highest mutational frequency of 0.1309 (25/191) and was distributed across all sampling sites. Correlation analyses indicated that no significant correlations were observed between all detected variant loci and MICs of isolates to itraconazole and voriconazole. Phylogenetic analysis revealed that the six sequence types of cyp51A in Guizhou tea plantations were broadly intermixed with those from other parts of China and outside of China. We discussed the implications of these results in the management of ARAF.