[Arthroderma benhamiae strains in Germany : Morphological and physiological characteristics of the anamorphs]

Abstract

Background: Anamorphs of Arthroderma (A.) benhamiae, which can cause inflammatory tinea lesions in humans, have been progressively spreading in Germany.

Objectives: Identification of A. benhamiae anamorphs by conventional methods.

Materials and methods: Evaluation of our own results obtained with A. benhamiae anamorphs and from the relevant literature.

Results: Infections with A. benhamiae anamorphs are usually transferred by guinea pigs or other animals. A. benhamiae anamorphs can be cultured on growth media used for dermatophytes and can be characterized morphologically and physiologically. In Germany the yellow variant is seen most often but a white variant that equals Trichophyton (T.) interdigitale has also been observed. On Sabouraud agar the yellow variant develops markedly yellow thalli, whereas the white variant produces white aerial mycelium. Microconidia are formed by the yellow variant-if at all-only scarcely and delayed; they are small, roundish, and arranged in a grape-like order. The white variant produces peg-shaped microconidia alongside hyphae as well as roundish ones in grape-like clusters, and subsequently some macroconidia, chlamydospores, and spiral hyphae. In microcultures with both variants circuit-like hyphal structures can consistently be demonstrated. On Trichophyton agars only the yellow variant is clearly dependent on thiamine. The urease test is negative with the yellow variant and positive with the white variant. Most strains of both variants are negative in the hair perforation test.

Conclusions: The characteristics described allow reliable identification of the yellow variant of the A. benhamiae anamorph by conventional methods; a distinction between the white variant and T. interdigitale can be more difficult. Dermatologists should be able to identify this agent in clinical routine.

Keywords: Circuit-like hyphal structures; Dermatophytes; Epidemiology; Physiology; Tinea.