Germrelated virulence factors15

Clostridia produce toxins - high molecular weight proteins with general or local effects - responsible of the severity of the clinical picture. The best known of these clostridial toxins is the alpha toxin secreted by Clostridium perfringens. It is a lethal, necrotizing and haemolytic toxin with predominant tissue effect due to great affinity for certain cellular structures not found in circulating blood. Alpha toxin is a C-type phospholipase (lecithinase) hydrolyzing lecithin into diglyceride and phosphoryl-choline. Lecithin is an essential component of the membranes of the eukaryotic cells. Its physiologic function is to stabilize the lipoprotein structure of cell membranes. So alpha toxin action affects all cells: muscle cells (myolysis); red blood cells (haemolysis); platelets (coagulation disorders); tubular renal cells (haemoglobinuria)12. Other toxins are also produced in varying amounts:13 beta, delta and theta toxins.

Non spore-forming anaerobic bacteria are comparatively less virulent than Clostridia because they do not produce such powerful exotoxins. They are actually opportunistic germs which can become pathogenic under certain circumstances16. Like Clostridia, these bacteria excrete various substances into their environment, some of which play an important part in the fast development and the necrotizing effect of these infections. Hence, some of those enzymes damage the tissue constituents (e.g., procollagenase, hyaluronidase, proteinase, etc.) enabling the destruction of the support structures of subcutaneous tissue and causing bacterial diffusion into the spaces formed along the fascia. Other enzymes (e.g., coagulase) cause local coagulation of the microvessels of the infected area followed propagating destruction as the local ischemia and promotes further bacterial proliferation.

Furthermore, some species of the bacteroides genus are enclosed in a polysaccharide capsule which protects them from phagocytosis. This constituent plays a major part in the pathogenicity of these bacteria. It has been experimentally proven that the intra-peritoneal injection of this purified capsular polysaccharide is all that is needed to induce abscess forming. This capsule also seems capable - at least in vitro - to inhibit the bactericidal activity of polymorphonuclear (PMN) leukocytes against certain aerobic bacteria and reducing their opsonization. This fact can account, in part, for the well-described synergy between aerobic and anaerobic bacteria17,18.

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