Objectives: In recent years, Aspergillus species taxonomy has been revolutionized with the introduction of the concepts of cryptic species and species complex. However, these “new” species remain usually rare and their characteristics, including antifungal susceptibility, are little known. Thus, the aim of this study was to collect a large number of isolates per cryptic species and to assess their antifungal susceptibility.
Methods: From September 2017, users of the MSI application, a free online MALDI-TOF massspectrometry database, were asked to send to our University Hospital, isolates they identified as cryptic species of Aspergillus. Identification at the species level was confirmed by sequencing a part of beta-tubulin and calmodulin genes. Antifungal susceptibility for azole drugs (itraconazole, voriconazole, posaconazole and isavuconazole) and amphotericin B was assessed by EUCAST broth microdilution reference method.
Results: During the study period, 192 isolates were collected from 11 centers in France and Denmark and were assessed for antifungal susceptibility. According to sequence-based identification, isolates corresponded to 43 species, belonging to 6 species complexes. Nidulantes species complex was the most represented (53 isolates, 12 species), followed by the species complexes Circumdati (43 isolates, 10 species) and Fumigati (40 isolates, 8 species). The last species complexes represented were Usti (23 isolates, 4 species), Flavi (19 isolates, 5 species) and Terrei (14 isolates, 4 species). Regarding the 3 main species complexes, diversity in antifungal susceptibility between cryptic species was observed. Indeed, inside the Fumigati complex A. thermomutatus, A. lentulus, A. udagawae, A. fischeri and (15, 7, 3 and 3 isolates respectively) showed pan-azole high minimal inhibitory concentrations (MICs), whereas A. hiratsukae (8 isolates) showed low MICs. All these species had low MICs for amphotericin B, except A. lentulus with MICs ³4 mg/L. Regarding the Circumdatispecies complex, A. westerdijkiae (12 isolates) showed the highest MICs for amphotericin B (> 16 mg/L), whereas A. sclerotiorum (17 isolates) showed lower MICs (MIC50 = 4 mg/L). In contrast A. sclerotiorum showed pan-azole high MICs, whereas azole MICs where much lower for A. westerdijkiae. Finally, inside the Nidulantescomplex, all species showed low MICs for all drugs, except A. creberand A. unguis (6 and 2 isolates respectively) which showed high MICs (> 8 mg/L) for itraconazole only. MICs regarding the 3 other species complexes studied are shown in table 1.
Conclusion: This study brings evidence on the diversity of antifungal susceptibility pattern inside the same species complex. However, including more isolates is needed to confirm these preliminary results. Nevertheless, this underline the importance of an accurate and easy-to-perform identification of Aspergillus at the species level for the management of Aspergillus diseases and the conduct of epidemiological studies.
Full conference title:
- TIMM (2019)