Nondermatophytic filamentous keratinophilic fungi and their role in human infection

Keratinophilic fungi include a variety of filamentous fungi mainly comprising hyphomycetes and several other taxonomic groups. Hyphomycetes include dermatophytes and a great variety of nondermatophytic filamentous fungi. Most of the latter occur as saprophytes in soil, and some are plant pathogens. Chrysosporium species are the commonest nondermatophytic filamentous fungi and are predominantly recovered from soil and other natural substrata by hairbaiting technique. C. tropicum and C. pannicola have been frequently isolated from human and animal skin lesions but their etiological relationship has not been established. Nattrassia mangiferae, a coelomycete with its anamorph as Scytalidium dimidiatum, is a well known plant pathogen, and has been frequently reported during the last three decades as an etiological agent of human skin and nail infections. Another species of Scytalidium, viz. S. hyalinum, regarded as an albino mutant of S. dimidiatum has also been frequently known to cause similar infections. Phoma, another coelomycete, includes several species pathogenic to humans. Among other nondermatophytic filamentous keratinophilic fungi known to cause human infections are species of Fusarium, Scopulariopsis, Aspergillus, Geotrichum, Alternaria, Curvularia, Onychocola, Microascus, Aphanoascus and Chaetomium. Several species of gymnoascaceous fungi, viz. Ctenomyces serratus, Gymnoascus reesii, G. intermedius and Gymnascella dankaliensis are often isolated from soil by hair-baiting technique; they have also been occasionally recovered from human skin lesions but without any evidence of etiological relationship. The criteria considered important for evaluating the role of nondermatophytic filamentous fungi in skin infections are the demonstration of mycelial elements in direct microscopy of skin scrapings or biopsy compatible with those in culture, repeated positive cultures from clinical material, and the exclusion of infection due to a dermatophyte or a fungus other than the one in question.