Microdilution in vitro antifungal susceptibility of Exophiala dermatitidis, a systemic opportunist

Badali H., De Hoog G.S., Mohseni S. and Meis J.F.


Backgrounds: The black yeast Exophiala dermatitidis is increasingly recognized as an etiologic agent of a diversity of invasive infections. Clinical pictures include, in addition to subcutaneous infections, pulmonary colonization of the lungs of patients with cystic fibrosis and disseminated, eventually and fatal disease in patients without known underlying disease or immune disorder. Also intestinal colonization has been reported. Given the apparent intrinsic virulence of the species, an increase in the frequency of opportunistic infections in compromised or elderly patients may be expected. The species' prevalence in the human-dominated environment is limited to particular foci, such as Turkish steam baths and petroleum oil-contaminated railway ties in the tropics. Despite worrying clinical pictures associated with E. dermatitidis, there is little information regarding the antifungal susceptibility patterns against currently available antifungal agents. Material &
Methods: Thus, the in vitro activities of eight antifungal agents against clinical (n = 66) and environmental (n = 15) strains of Exophiala dermatitidis were obtained. The Clinical and Laboratory Standards Institute (CLSI) provides no specific guidelines for testing the in vitro antifungal susceptibility of this fungus. No other testing protocol has also been validated for testing the susceptibility of E. dermatitidis.
Results: In the present study, the resulting MIC90s for all strains (n = 81) were as follows, in increasing order: posaconazole, 0.125 μg ml-1; itraconazole, 0.25 μg ml-1; voriconazole, 0.5 μg ml-1; amphotericin B, 0.5 μg ml-1; Isavuconazole, 1 μg ml-1; caspofungin, 8 μg ml-1 anidulafungin, 8 μg ml-1 and fluconazole, 16 μg ml-1, without any significant differences in the pattern of susceptibility between environmental and clinical strains (P > 0.05) and genotypes A and B (P > 0.05). The difference in the MIC90s between the two groups of isolates did not differ by more than one dilution. Discussion: Therefore, the present study based on in vitro activity showed that posaconazole and itraconazole might have a potent activity with a best choice of alternative to amphotericin B, for E. dermatitidis cerebral phaeohyphomycosis. In addition, the un-marketing agent Isavuconazole, which is also available as an intravenous preparation, has adequate activity against the latter agent. However, their clinical effectiveness in the treatment of Exophiala dermatitidis infections remains to be determined.

    • TIMM 5th (2013)