Current hypotheses on synergistic microbial gangrene.

We have reviewed spreading infections of the dermis, with special reference to the importance of synergy in their causation. Evidence for this is accumulating from both clinical studies and from studies in laboratory animals. Necrotizing fasciitis (rapid spread over 24 h) can be caused by beta-haemolytic streptococci, sometimes with Staphylococcus aureus, or by mixed infections of aerobes and anaerobes, often of gut origin. Animal studies provide good evidence that S. aureus can potentiate the beta-haemolytic streptococcal infection in necrotizing fasciitis. There is also evidence that mixtures of aerobes and anaerobes can act synergistically, but animal models for necrotizing fasciitis have not been developed. Anaerobic cellulitis (variable rate of spread from hours to days) can be caused by mixed aerobes and anaerobes or by mixed clostridia. Animal studies provide good evidence for synergy in the former. Meleney's synergistic postoperative gangrene (slow spread over weeks) may be cutaneous amoebiasis: the animal model of Brewer and Meleney relates to the more rapid infections of anaerobic cellulitis.