A five-year survey of dematiaceous fungi in a tropical hospital reveals potential opportunistic species

Abstract

Dematiaceous fungi (black fungi) are a heterogeneous group of fungi present in diverse environments worldwide. Many species in this group are known to cause allergic reactions and potentially fatal diseases in humans and animals, especially in tropical and subtropical climates. This study represents the first survey of dematiaceous fungi in Malaysia and provides observations on their diversity as well as in vitro response to antifungal drugs. Seventy-five strains isolated from various clinical specimens were identified by morphology as well as an internal transcribed spacer (ITS)-based phylogenetic analysis. The combined molecular and conventional approach enabled the identification of three classes of the Ascomycota phylum and 16 genera, the most common being Cladosporium, Cochliobolus and Neoscytalidium. Several of the species identified have not been associated before with human infections. Among 8 antifungal agents tested, the azoles posaconazole (96%), voriconazole (90.7%), ketoconazole (86.7%) and itraconazole (85.3%) showed in vitro activity (MIC ≤ 1 µg/mL) to the largest number of strains, followed by anidulafungin (89.3%), caspofungin (74.7%) and amphotericin B (70.7%). Fluconazole appeared to be the least effective with only 10.7% of isolates showing in vitro susceptibility. Overall, almost half (45.3%) of the isolates showed reduced susceptibility (MIC >1 µg/mL) to at least one antifungal agent, and three strains (one Pyrenochaeta unguis-hominis and two Nigrospora oryzae) showed potential multidrug resistance.

Figure 1. Microscopic features of dematiaceous fungi.

(A-D) Macroconidia of Curvularia, Bipolaris, Exserohilum and Alternaria (E) Arthroconidia of Neosyctalidium (F) Globose chain conidia and ramoconidia of Cladosporium (G) conidia of Daldinia (H) Dark conidia of Nigrospora (I) Chaetomium perithecium covered with long setae and dark ascospores (J) Spine-like conidiophore and hyaline conidia of Exophiala (K) Ochroconis two-celled clavate conidia with cylindrical conidiophore. Bars 20 µm.

Figure 2. Classifications of fungal isolates.

Bayesian tree generated with general time reversible (GTR) model space based on unique ITS1-5.8S-ITS2 gene sequences with two strains of Saccharomyces boulardii as out-group. Isolate sequence duplicates are listed in parentheses next to their representative. Clinical isolates from UMMC used in this study are printed in bold. Bayesian posterior probability values for every clustering are printed on each node.