Agents of Mycetoma

Mycetoma is a chronic progressive granulomatous infection of the skin and subcutaneous tissue most often affecting the lower extremities, typically a single foot. Disease is unique from other cutaneous or subcutaneous diseases in its triad of localized swelling, underlying sinus tracts, and production of grains or granules (comprised of aggregations of the causative organism) within the sinus tracts. These infections may be caused by fungi and termed eumycotic mycetoma or eumycetoma, or by filamentous higher bacteria, termed actinomycotic mycetoma or actinomycetoma. The term mycetoma can also be found in the literature incorrectly referring to a fungus ball found in a preexisting cavity in the lung or within a paranasal sinus, most often caused by Aspergillus spp. Grain formation by infecting organisms is restricted to the diseases mycetoma, actinomycosis (see Chapter 255), and botryomycosis. Actinomycosis is a disease produced by the anaerobic and microaerophilic higher bacteria that normally colonize the mouth and gastrointestinal and urogenital tracts. The portal of entry in actinomycosis is from those colonized sites, whereas in mycetoma the portal is the skin and subcutaneous tissue into which the organism was inoculated by minor trauma. Botryomycosis is a chronic bacterial infection of soft tissues in which the causative organism, often Staphylococcus aureus, is found in loose clusters among the pus. In a rare form of ringworm called dermatophyte mycetoma, there are also loosely compacted clusters of hyphae in subcutaneous pus. In contrast, mycetoma grains are dense clusters of organisms.