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Journal of Clinical Microbiology, August 2004, p. 3789-3794, Vol. 42, No. 8
0095-1137/04/$08.00+0 DOI: 10.1128/JCM.42.8.3789-3794.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Dermatology Department, St John's Institute of Dermatology, Guy's Hospital, Guy's, Kings and St Thomas' Medical Schools,1 Department of Microbiology, St Thomas' Hospital, London, United Kingdom,3 Microbiology Department, Chiang-Mai Medical School, Chiang-Mai, Thailand,2 Department of Medicine,4 Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York5
Received 15 January 2004/ Returned for modification 11 March 2004/ Accepted 7 April 2004
Scytalidium dimidiatum is a pigmented dematiaceous coelomycete that typically causes chronic superficial skin diseases and onychomycosis, as well as deeper infections, such as subcutaneous abscesses, mycetoma, and even fungemia in immunocompromised patients. A second species, Scytalidium hyalinum, has hyaline hyphae and arthroconidia and is considered by some authors to be an albino mutant of S. dimidiatum. This study aimed to confirm the presence of melanin or melanin-like compounds (which have been previously implicated in the virulence of other fungal pathogens) in S. dimidiatum from a patient with multiple subcutaneous nodules. Treatment of the hyphae and arthroconidia with proteolytic enzymes, denaturant, and concentrated hot acid yielded dark particles, which were stable free radicals, consistent with their identification as melanins. Extracted melanin particles from S. dimidiatum cultures were labeled by melanin-binding monoclonal antibodies (MAbs) from Sporothrix schenckii, Aspergillus fumigatus, and Cryptococcus neoformans. Lesional skin from the patient infected with S. dimidiatum contained fungal cells that were labeled by melanin-binding MAbs, and digestion of the tissue yielded dark particles that were also reactive. S. hyalinum was also subjected to the melanin extraction protocol, but no dark particles were yielded.
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