Genetic Diversity and <i>In Vitro</i> Antifungal Susceptibility of 200 Clinical and Environmental Aspergillus flavus Isolates

Abstract

<i>Aspergillus flavus</i> has been frequently reported as the leading cause of invasive aspergillosis in certain tropical and subtropical countries. Two hundred <i>A. flavus</i> strains originating from clinical and environmental sources and collected between 2008 and 2015 were phylogenetically identified at the species level by analyzing partial β-tubulin and calmodulin genes. <i>In vitro</i> antifungal susceptibility testing was performed against antifungals using the European Committee on Antimicrobial Susceptibility Testing (EUCAST) broth microdilution method. In addition, genotyping was performed using a short-tandem-repeat (STR) assay of a panel of six microsatellite markers (<i>A. flavus</i> 2A, 2B, 2C, 3A, 3B, and 3C), in order to determine the genetic variation and the potential relationship between clinical and environmental isolates. The geometric means of the minimum inhibitory concentrations/minimum effective concentrations (MICs/MECs) of the antifungals across all isolates were (in increasing order): posaconazole, 0.13 mg/liter; anidulafungin, 0.16 mg/liter; itraconazole, 0.29 mg/liter; caspofungin, 0.42 mg/liter; voriconazole, 0.64 mg/liter; isavuconazole, 1.10 mg/liter; amphotericin B, 3.35 mg/liter; and flucytosine, 62.97 mg/liter. All of the clinical isolates were genetically different. However, an identical microsatellite genotype was found between a clinical isolate and two environmental strains. In conclusion, posaconazole and anidulafungin showed the greatest <i>in vitro</i> activity among systemic azoles and echinocandins, respectively. However, the majority of the <i>A. flavus</i> isolates showed reduced susceptibility to amphotericin B. Antifungal susceptibility of <i>A. flavus</i> was not linked with the clinical or environmental source of isolation. Microsatellite genotyping may suggest an association between clinical and environmental strains, although this requires further investigation.