| Abstract: | Phylogenetic analyses of sequences generated from portions of three genes coding for the proteins enolase (enoA), β-tubulin (benA), and calmodulin (calM) of a large number of isolates within the section Terrei, genus Aspergillus, revealed the presence of a new cryptic species within this section, Aspergillus alabamensis. Most members of this new cryptic species were recovered as colonizing isolates from immunocompetent patient populations, had decreased in vitro susceptibilities to the antifungal drug amphotericin B, and were morphologically similar to but genetically distinct from Aspergillus terreus isolates.Invasive infections caused by Aspergillus terreus are often disseminated with increased lethality compared with infections caused by other Aspergillus species and tend to be resistant to treatment with the antifungal drug amphotericin B (6, 14, 17). Despite the clinical significance of this organism, little is known about the epidemiology, genetic diversity, and population structure of A. terreus.Historically, A. terreus has been identified in the laboratory by conventional methods such as colony morphology and microscopic characteristics. Such morphological studies have placed A. terreus as a single homogenous species within the section Terrei along with two other varieties, A. terreus var. africanus and A. terreus var. aureus (11). Recent studies have shown that morphological characteristics may not be reliable for distinguishing Aspergillus species, as inferred from the demonstration of multiple cryptic species within the section Fumigati by molecular phylogenetic methods (3-5, 13, 18).In the past, molecular methods largely based on randomly amplified polymorphic DNA-PCR-based assays have shown that A. terreus isolates can have great strain diversity (1, 8, 16). One recent genotyping study of several A. terreus clinical isolates recovered from two different medical centers using this method concluded that nosocomial acquisition of A. terreus infections was highly unlikely given the great genetic diversity observed (7). Another study demonstrated that comparative sequence analyses of the D1 and D2 regions had limited utility to study relationships within the section Terrei, while the internal transcribed spacer regions were useful since there was more nucleotide diversity in this region (16). However, the authors of this study could not resolve species within the section Terrei using these molecular approaches.In the present study, we have developed a multilocus sequence approach employing three protein-coding regions to study species diversity of the section Terrei using a large panel of isolates from both clinical and environmental origins recovered from various parts of the world. The studies outlined below demonstrate the presence of a new, clinically relevant species, Aspergillus alabamensis, and clarify the taxonomic position of the A. terreus variant A. terreus var. aureus. |
