A case of an autochthonous toenail infection caused by Hendersonula toruloidea is presented. H. toruloidea was characterized by thick, branching septate brown-walled hyphae of a non-dermatophyte in microscopic tissue mounts in 25% Na0H with 5% glycerol. Cultures grew out on Littman's agar and Sabouraud peptone glucose agar plus chloramphenicol, but only if cycloheximide was not present. In vitro, the H. toruloidea isolate was characterized by copious 1-to 2-celled hyaline to dark-brown arthroconidia deriving from the fragmentation of aerial hyphae. It is likely that more infections due to H. toruloidea will be diagnosed if cycloheximide-free media are routinely used in the isolation of organisms from suspected dermatophyte infections.

Arthroconidia produced by dermatophytic fungi are considered to be the primary cause of skin and nail infections in humans and animals. Trichophyton rubrum is currently the most common cause of tinea pedis all over the world. The common form of T. rubrum produces a cottony colony in cultures that is characteristically low in conidia formation. The attempts to produce arthroconidia in T. rubrum have shown little success so far. Recently, Trichophyton raubitschekii, an anthropophilic dermatophyte prevalent in Asia, Africa, and the Mediterranean, has been recognized as a variant of T. rubrum. In cultures, T. raubitschekii is characterized by a granular colony form, and an abundance of both micro- and macroconidia. The present study reveals a predominance of arthroconidia in two T. raubitschekii cultures isolated from clinical materials. These isolates were able to maintain arthroconidiation in bimonthly subcultures throughout the entire course of this study. The growth parameters for in vitro cultivation of arthroconidia are described here. Arthroconidia prepared from T. raubitschekii cultures showed greater than 95% germination within 21 h of suspension in phosphate-buffered saline. The availability of arthroconidia in T. raubitschekii cultures appears to offer a practical means of characterizing infective cells in T. rubrum.

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