Cutaneous infections: microbiologic and epidemiologic considerations.

The normal bacterial flora of the skin represents an important host defense mechanism against invasion by potentially pathogenic organisms. This flora is primarily composed of aerobic diphtheroids (Corynebacterium species), anaerobic diphtheroids (Propriono-bacterium acnes), and coagulase-negative staphylococci. Gram-negative bacilli may be present in limited numbers in intertriginous areas. Localized cutaneous infections occur in ostensibly normal hosts, often after trivial trauma, examples being streptococcal or staphylococcal impetigo, staphylococcal furunculosis, or more unusual infections due to agents such as Mycobacterium marinum. When the skin is injured more extensively by trauma, burns, ischemia with ulceration, or iatrogenic manipulations, or when host immunologic defenses are suppressed, more severe infections are likely to supervene, and the threat of systemic dissemination of infecting microorganisms increases. Cutaneous infection in immunosuppressed hosts may involve the same pyogenic bacteria that affect normal subjects or it may involve a variety of opportunistic invaders, including herpes viruses, gram-negative bacilli, mycobacteria, and deep or superficial mycoses. The skin may also be affected by infections whose primary site lies elsewhere in the body. Cutaneous manifestations may be secondary to hematogenous seeding of the causative agent or to the effects of toxins or immune complexes. Certain microbial agents may initiate a wide variety of cutaneous lesions, depending on route of infection and the status of the host. Thus, cutaneous lesions attributable to Pseudomonas aeruginosa range from "green nail syndrome" and self-limited folliculitis to ecthyma gangrenosum. Similarly, group A streptococci may produce pyoderma, cellulitis, lymphangitis, erysipelas, or scarlet fever. We recently described a syndrome of recurrent cellulitis in the saphenous vein donor extremities of patients who have undergone coronary artery bypass grafts. Most patients have associated tinea pedis. The pathophysiologic aspects of this syndrome are probably multifactorial, involving compromise of lymphatic or venous drainage, bacterial infection, elaboration of bacterial toxins, and hypersensitivity to bacterial or fungal products, or both. Coagulase-negative staphylococci are exhibiting a more prominent pathogenic potential than heretofore. When they infect immunosuppressed hosts or patients with indwelling intravascular catheters or cardiac prostheses, coagulase-negative staphylococci may cause life-threatening disease.(ABSTRACT TRUNCATED AT 400 WORDS)