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

The in vitro activities of eight antifungal agents were determined against clinical (n = 63 genotype A, n = 3 genotype B) and environmental (n = 2 genotype A, n = 13 genotype B) strains of Exophiala dermatitidis. The resulting MIC(90)s for all strains (N = 81) were, in increasing order, as follows: posaconazole, 0.125 µg/ml; itraconazole, 0.25 µg/ml; voriconazole, 0.5 µg/ml; amphotericin B, 0.5 µg/ml; isavuconazole, 1 µ/ml; caspofungin, 8 µg/ml; anidulafungin, 8 µg/ml and fluconazole, 16 µg/ml. There were no significant differences in the patterns of susceptibility between genotypes A and B, environmental and clinical strains, isolates recovered from cutaneous and deep locations and strains from different geographical areas (P > 0.05). The difference in the MIC(90)s between each of these groups was not more than one dilution. The present study demonstrated that, based on in vitro activity, posaconazole and itraconazole have the highest activity against this fungus. In addition, voriconazole and the experimental broad-spectrum antifungal triazole, isavuconazole, both of which are available as intravenous preparations, have adequate activity against E. dermatitidis. However, in vivo efficacy remains to be determined.

Fatal Exophiala infections in China, with a report of seven cases.

During the past four decades, seven patients were documented in China to have died from Exophiala infections. Causative agents were Exophiala dermatitidis, Exophiala spinifera, Exophiala jeanselmei and a new Exophiala species, Exophiala asiatica. We retrospectively analysed the clinical characteristics of these infections in China and confirmed the identity of aetiological agents of Chinese fatal cases using rDNA ITS sequence analysis. While E. dermatitidis displayed neurotropism, E. spinifera showed osteotropism. The other two species, E. jeanselmei and E. asiatica had caused brain infections in China.

Rapid screening for genotypes as possible markers of virulence in the neurotropic black yeast Exophiala dermatitidis using PCR-RFLP.

A simple method for fungal genotype screening was developed for the black yeast Exophiala dermatitidis based on RFLP of ribosomal ITS regions currently used as potential virulence markers. In a study set of 502 strains of the species, two main genotypes were recognized. Only 0.97% of lanes were difficult to interpret as they did not clearly present one of the expected genotypes. Twenty strains were deviating and proved to be E. spinifera after sequencing. Eight common, related species (based on SSU data) with clinical significance yielded different patterns with TaqI digestion, and thus the method is also usable for routine diagnostics.

Redefinition of Aureobasidium pullulans and its varieties.

Using media with low water activity, a large numbers of aureobasidium-like black yeasts were isolated from glacial and subglacial ice of three polythermal glaciers from the coastal Arctic environment of Kongsfjorden (Svalbard, Spitsbergen), as well as from adjacent sea water, sea ice and glacial meltwaters. To characterise the genetic variability of Aureobasidium pullulans strains originating from the Arctic and strains originating pan-globally, a multilocus molecular analysis was performed, through rDNA (internal transcribed spacers, partial 28 S rDNA), and partial introns and exons of genes encoding beta-tubulin (TUB), translation elongation factor (EF1alpha) and elongase (ELO). Two globally ubiquitous varieties were distinguished: var. pullulans, occurring particularly in slightly osmotic substrates and in the phyllosphere; and var. melanogenum, mainly isolated from watery habitats. Both varieties were commonly isolated from the sampled Arctic habitats. However, some aureobasidium-like strains from subglacial ice from three different glaciers in Kongsfjorden (Svalbard, Spitsbergen), appeared to represent a new variety of A. pullulans. A strain from dolomitic marble in Namibia was found to belong to yet another variety. No molecular support has as yet been found for the previously described var. aubasidani. A partial elongase-encoding gene was successfully used as a phylogenetic marker at the (infra-)specific level.

The neurotropic black yeast Exophiala dermatitidis has a possible origin in the tropical rain forest.

The black yeast Exophiala dermatitidis is known as a rare etiologic agent of neurotropic infections in humans, occurring particularly in East and Southeast Asia. In search of its natural habitat, a large sampling was undertaken in temperate as well as in tropical climates. Sampling sites were selected on the basis of the origins of previously isolated strains, and on the basis of physiological properties of the species, which also determined a selective isolation protocol. The species was absent from outdoor environments in the temperate climate, but present at low abundance in comparable habitats in the tropics. Positive outdoor sites particularly included faeces of frugivorous birds and bats, in urban as well as in natural areas. Tropical fruits were found E. dermatitidis positive at low incidence. Of the human-made environments sampled, railway ties contaminated by human faeces and oily debris in the tropics were massively positive, while the known abundance of the fungus in steam baths was confirmed. On the basis of the species' oligotrophy, thermotolerance, acidotolerance, moderate osmotolerance, melanization and capsular yeast cells a natural life cycle in association with frugivorous animals in foci in the tropical rain forest, involving passage of living cells through the intestinal tract was hypothesized. The human-dominated environment may have become contaminated by ingestion of wild berries carrying fungal propagules.

Intestinal prevalence of the neurotropic black yeast Exophiala (Wangiella) dermatitidis in healthy and impaired individuals.

A screening of 2300 samples of faeces from humans with and without underlying disease revealed that the black yeast Exophiala dermatitidis is present at a frequency of 5.2 per thousand (n=12). Eight individuals positive for the fungus had diarrhoea at the moment of its isolation, out of 11 where relevant information was available. Judging from repeated isolation over several weeks in one patient, the organism is able to persist in the human intestinal tract.

Characterization of Aureobasidium pullulans isolated from airborne spores in Thailand.

Isolates from air in several locations in Thailand were identified as Aureobasidium pullulans PR with dark pigmentation (Loei province), A. pullulans SU with an unusual conidial apparatus (Chiangmai province), and A. pullulans CU with burgundy-red pigmentation (from a shady area in Bangkok). The internal transcribed spacer sequences of the rDNA of A. pullulans SU and A. pullulans CU confirmed that they were A. pullulans. Both A. pullulans CU and A. pullulans PR preferred 30 degrees C and pH 7.5 for exopolysaccharide (EPS) production, while A. pullulans SU preferred 25 degrees C and pH 6.5. All three isolates preferred glucose over sucrose and (NH(4))(2)SO4 over peptone for EPS production. Under optimal conditions, A. pullulans PR produced EPS yields of up to 0.225 g g(-1), followed by A. pullulans CU (0.185 g g(-1)) and A. pullulans SU (0.158 g g(-1)). Amylase activities were detected during the course of EPS production but gradually decreased as the EPS yields increased. IR spectra suggest that the EPS from these isolates was pullulan. EPS from the three isolates were partially sensitive to pullulanase.