Identification of Aspergillus species using internal transcribed spacer regions 1 and 2.

Abstract

Aspergillus species are the most frequent cause of invasive mold infections in immunocompromised patients. Although over 180 species are found within the genus, 3 species, Aspergillus flavus, A. fumigatus, and A. terreus, account for most cases of invasive aspergillosis (IA), with A. nidulans, A. niger, and A. ustus being rare causes of IA. The ability to distinguish between the various clinically relevant Aspergillus species may have diagnostic value, as certain species are associated with higher mortality and increased virulence and vary in their resistance to antifungal therapy. A method to identify Aspergillus at the species level and differentiate it from other true pathogenic and opportunistic molds was developed using the 18S and 28S rRNA genes for primer binding sites. The contiguous internal transcribed spacer (ITS) region, ITS 1-5.8S-ITS 2, from referenced strains and clinical isolates of aspergilli and other fungi were amplified, sequenced, and compared with non-reference strain sequences in GenBank. ITS amplicons from Aspergillus species ranged in size from 565 to 613 bp. Comparison of reference strains and GenBank sequences demonstrated that both ITS 1 and ITS 2 regions were needed for accurate identification of Aspergillus at the species level. Intraspecies variation among clinical isolates and reference strains was minimal. Sixteen other pathogenic molds demonstrated less than 89% similarity with Aspergillus ITS 1 and 2 sequences. A blind study of 11 clinical isolates was performed, and each was correctly identified. Clinical application of this approach may allow for earlier diagnosis and selection of effective antifungal agents for patients with IA.