Report

With nearly 60 participants from 19 countries the workshop inaugurating the ISHAM Working Groups “Black Yeasts and Related Fungi” and “Chromoblastomycosis” was a great success. In a pleasant and relaxed atmosphere a large number of presentations were given, nearly all containing new, unpublished material – enough to fill a special issue of ‘Studies in Mycology’ and one of ‘Medical Mycology’, both scheduled for publication Spring 2008. The workshop united very different disciplines, covering clinical problems but also environmental aspects and biotechnology. This has lead to much more understanding of the pathology, virulence, and routes of infection of these remarkable organisms.

The workshop was subdivided in several main themes, the first of which was extremotolerance. Bizarre types of ecology and evolution were shown, such as in Arctic glaciers, Mediterranean rock, in pure acid, and in nearly saturated salt solutions. The evolutionary origin of opportunistic black yeasts is supposed to be located in rock-inhabiting lichens. Factors enhancing their survival may also contribute to virulence in other black yeasts, but is certainly not the only factor. A relic of extremotolerance was found in Cladophialophora agents of human chromoblastomycosis, which have a reservoir in spines of cactus plants in semi-arid climates of South America. Development of pathogenic abilities in members of the order Chaetothyriales seems to coincide with loss of sexuality: all opportunistic Exophiala species investigated proved to be clonal. 

The natural niche of opportunistic black yeasts remains puzzling. They are not commonly isolated from the environment, but seem to live in rather weird habitats, such as on creosote-treated wood, in biofilters, and in steam baths. This suggests that hitherto unknown, unique factors determine the shift towards opportunism. It has been put forward that assimilation of monoaromatic toxins might be one of these factors. The preference for such compounds is now successfully being applied for selective isolation of black yeasts.
The spectrum of diseases caused by Chaetothyrialean black yeasts is remarkable: in no other fungal group pathology is such a consistent phenomenon with such a diversity of clinical syndromes. Diseases range from superficial to systemic, in the latter case very often in otherwise apparently healthy patients. Predilection differs with the species. Prevalence in cutaneous samples and in lungs of patients with pulmonary disorders is actually quite high, but the agents are frequently overlooked. A remarkable feature connecting disease in warm- and cold-blooded animals is the occurrence of fish-associated species in skin infections of human extremities with poor blood circulation.

Chromoblastomycosis is a unique disease entity, occurring only in the black yeast order Chaetothyriales, and there even limited to only four species, which are not each other’s nearest neighbours. Understanding of the disease is of great clinical as well as fundamental relevance. Good overviews were presented, demonstrating the clinical diversity of the disease. Fungi morphologically similar to the etiologic agents of disease can be isolated from rotten plants in the vicinity of the patients, but molecular data prove that they are not identical. Species occurring in cactus spines seems to have given rise to agents of chromoblastomycosis, whereby the human host shows an adaptive cellular immune response suggesting a shift to primary pathogenicity. The high frequency of the disease in endemic areas is a major public health problem.

Subsequent presentations on black yeasts will be organized at TIMM-3 in Torino, Italy, 28-31 October, 2007, and at IUMS-12 in Istanbul, Turkey, 5-8 August 2008.