Molecular Characterization and Antifungal Profiling of Nine Phenotypic Aspergillus nidulans Isolates: A Case Series From North India

ABSTRACT

Aspergillus nidulans is a fungal pathogen that causes respiratory issues in individuals with compromised immune systems. It is identified through culture characteristics and microscopic features such as Cleistothecia and Hülle Cells. However, similar traits are found in cryptic Aspergillus species, such as stellatus, cristatus , and oryzae . In a case series from a hospital in North India, A. nidulans strains isolated from patients with pulmonary aspergillosis were phenotypically identified and then underwent molecular characterization through sequencing of the amplified ITS1‐5.8S rDNA‐ITS2 region and antifungal susceptibility testing (AST) according to the CLSI M38A3 guidelines. The molecular characteristics and antifungal profiles of the nine phenotypic A. nidulans were as follows: A. stellatus ( n  = 5), A. nidulans ( n  = 2), A. cristatus ( n  = 1), and A. oryzae ( n  = 1). Phylogenetic analysis revealed a close relationship between A. stellatus, A. nidulans , and A. cristatus , while A. oryzae showed significant divergence. Furthermore, the minimum inhibitory concentration (MIC) of antifungals was the lowest for caspofungin, followed by voriconazole. However, a higher amphotericin B MIC (2 µg/mL) was observed for A. stellatus . Thus, sequencing the ITS1‐5.8S rDNA‐ITS2 region can accurately identify cryptic species with superior taxonomic resolution. Additionally, the MIC of amphotericin B against A. stellatus underscores the importance of precise molecular identification and antifungal MIC profiling in each case of pulmonary aspergillosis.