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[Cellulitis and necrotizing fasciitis: microbiology and pathogenesis].

Streptococcus pyogenes is a common cause of necrotizing cutaneous infections in otherwise healthy children and adults. Several surface components are involved in the processes of adherence and invasiveness, such as protein M and capsulae. Streptolysin O and other bacterial products, such as pyrogenic exotoxins, are involved in tissue injury and necrosis. Toxins A and C act as superantigens and are expressed by strains associated with the toxic shock syndrome. Staphylococcus aureus, alone or in association with streptococci, is also commonly isolated form all body sites, but bacteremia is inconstant. Capsule, protein A, and the staphylococcal toxic shock syndrome toxin are the major pathogenicity factors. In infections of the face and the neck, the predominant anaerobes recovered in association with group A streptococci are Peptostreptococcus magnus, oral Prevotella, Porphyromonas spp., and Fusobacterium spp. Bacteroides fragilis, Clostridium, enterobacteria, and enterococci are recovered in infections located next to the perineal area. Penicillin is the drug of choice for the treatment of streptococcal infections. However benzylpenicillin may be not sufficient for severe infections and large inoculum, therefore the administration of clindamycin or another inhibitor of protein synthesis is recommended. Since the infection may be polymicrobial, the initial therapy should include treatment for staphylococci and anaerobes. In some cases broad- spectrum antibiotics also, effective on enterobacteria, are needed. The efficacy of appropriate parenteral antibiotics, however, depends on the prompt and aggressive exploration and debridement of suspected deep-seated infection, and supportive care of shock and multiple organ failure.