Taxonomy and Antifungal Susceptibility of Clinically Important Rasamsonia Species

Abstract

fIn recent years, Geosmithia argillacea has been increasingly reported in humans and animals and can be considered an emerging pathogen. The taxonomy of Geosmithia was recently studied, and Geosmithia argillacea and related species were transferred to the new genus Rasamsonia. The diversity among a set of Rasamsonia argillacea strains, including 28 clinical strains, was studied, and antifungal susceptibility profiles were generated. Data obtained from morphological studies and from phylogenetic analyses of internal transcribed spacer (ITS) and partial ␤-tubulin and calmodulin sequences revealed the presence of four species in the Rasamsonia argillacea complex, two of which are newly described here: R. piperina sp. nov. and R. aegroticola sp. nov. In contrast to other related genera, all Rasamsonia species can be identified with ITS sequences. A retrospective identification was performed on recently reported clinical isolates from animal or human patients. Susceptibility tests showed that the antifungal susceptibility profiles of the four members of the R. argillacea complex are similar, and caspofungin showed significant activity in vitro, followed by amphotericin B and posaconazole. Voriconazole was the least active of the antifungals tested. The phenotypically similar species R. brevistipitata and R. cylindrospora had different antifungal susceptibility profiles, and this indicates that correct species identification is important to help guide appropriate antifungal therapy.

Long-Term Rasamsonia argillacea Complex Species Colonization Revealed by PCR Amplification of Repetitive DNA Sequences in Cystic Fibrosis Patients

“…Apart from 16 of the isolates studied which had been previously identified by ITS 1 and 2 regions and beta-tubulin and calmodulin gene sequencing (8,13), species identification was performed by PCR amplification of part of the beta-tubulin gene (TUB locus). After grinding the mycelium in liquid nitrogen, DNA was extracted using the DNeasy plant minikit (Qiagen, Courtabeuf, France), and the TUB locus was amplified as previously described (22).…”

“…In CF patients, all species of the R. argillacea complex except R. eburnea have been reported to colonize the airways (8). While no clear relationship was established in the CF context between the colonization of the airways by these fungi and a clinical or functional deterioration, the recent report of R. argillacea pathogenicity in one patient with CF prompts further investigation (14).…”

“…However, members of the genus Rasamsonia, particularly those belonging to the R. argillacea species complex, are difficult to identify precisely in a routine clinical setting because of the lack of specific traits in their macroscopic and microscopic morphology. Therefore, sequencing of the internal transcribed spacer (ITS) 1 and 2 regions of ribosomal DNA, or of part of the beta-tubulin or calmodulin genes, is required for accurate species identification within the R. argillacea complex (7,8). Nevertheless, these methods are timeconsuming and do not allow strain differentiation for epidemiological purposes.…”

“…While no clear relationship was established in the CF context between the colonization of the airways by these fungi and a clinical or functional deterioration, the recent report of R. argillacea pathogenicity in one patient with CF prompts further investigation (14). In addition, differences between these closely related species in their antifungal susceptibility profiles further emphasize the need for an accurate identification of the fungus for optimal therapy (1,8). However, members of the genus Rasamsonia, particularly those belonging to the R. argillacea species complex, are difficult to identify precisely in a routine clinical setting because of the lack of specific traits in their macroscopic and microscopic morphology.…”

“…However, multilocus sequence analysis of several R. argillacea isolates revealed a clustering which superimposed some phenotypic differences. Therefore, R. argillacea is now considered a species complex comprising four distinct species: R. argillacea sensu stricto, R. piperina, R. aegroticola, and R. eburnea (8).…”