Occasionally, however, the resident skin flora causes cutaneous infections, especially with trauma or alterations in the stratum corneum. Examples are erythrasma, pitted keratolysis, trichomycosis axillaris, and most cases of cutaneous abscesses. In other sites, however, the predominant organisms are anaerobes, either alone or in the mixture of anaerobes and aerobes that constitutes the normal regional flora, including that from adjacent mucous membranes. These organisms ordinarily possess little virulence, but when introduced into the dermis or subcutaneous tissue by trauma or through a disrupted cutaneous surface, they may become pathogenic. Cutaneous abscesses usually cause a painful, fluctuant, red, tender swelling, on which may rest a pustule.
Treatment is incision and drainage of the area.
Gram's stain and culture of the pus are ordinarily unnecessary, as are topical antimicrobials. Systemic antibiotics are reserved for patients with extensive surrounding cellulitis, neutropenia, cutaneous gangrene, or systemic manifestations of infection, such as high fever. Erythrasma Corynebacterium minutissimum, a gram-positive bacillus that is part of the normal cutaneous flora, may cause a superficial, usually asymptomatic, skin infection called erythrasma. The most common site of erythrasma is between the toes, especially in the fourth interdigital space, where it causes fissuring, maceration, and scaling, resembling tinea pedis. Other locations are intertriginous areas, such as the axillae, groin, submammary area, and intergluteal cleft.