Elucidation of distribution patterns and possible infection routes of the neurotropic black yeast Exophiala dermatitidis using AFLP

Distribution of populations of the opportunistic black yeast Exophiala dermatitidis was studied using AFLP. This fungus has been hypothesized to have a natural habitat in association with frugivorous birds and bats in the tropical rain forest, and to emerge in the human-dominated environment, where it occasionally causes human pulmonary or fatal disseminated and neurotropic disease. The hypothesis of its natural niche was investigated by comparing a set of 178 strains from natural and human-dominated environments in Thailand with a worldwide selection of 107 strains from the reference collection of the CBS Fungal Biodiversity Centre, comprising 75.7% clinical isolates. Many isolates had unique AFLP patterns and were too remote for confident comparison. Eight populations containing multiple isolates could be distinguished, enabling determination of geographic distributions of these populations. Some of the populations were confined to Thailand, while others occurred worldwide. The local populations from Thailand contained strains from natural and urban environments, suggesting an environmental jump of the fungus. Strains from human brain belonged to widely dispersed populations. In some cases cerebral isolates were identical to isolates from the human intestinal tract. The possibility of cerebral infection through intestinal translocation was thus not excluded.