Gram-positive sepsis. Mechanisms and differences from gram-negative sepsis

This article has reviewed the mechanisms by which gram-positive bacteria lead to septic shock, with regard to bacterial structure and toxicology and the host responses elicited both in animal models and in the clinical setting. Gram-positive organisms are better suited to invade host tissues and elicit, in general, a brisker phagocytic response than gram-negative organisms. The lack of endotoxin in the outer cell wall is compensated for by the presence of exposed peptidoglycan and a range of other toxic secreted products. It appears that cell wall components of gram-positive bacteria may signal via the same receptor as gram-negative endotoxin, although the type of signal and coreceptor may differ. Both animal and clinical data suggest that, unlike endotoxin-mediated shock, gram-positive infection produces a modest TNF response only and does not respond well to anti-TNF therapies. This leads one to conclude that the mechanisms leading to shock in gram-positive infection may be multifactorial and perhaps more difficult to treat. A thorough review of gram-positive mechanisms of sepsis is hampered by a lack of basic research in this field. Understanding of gram-negative bacterial structure and the regulation of virulence genes is at an advanced stage, yet the molecular tools to analyse virulence factors in the gram-positive genome have only recently become available. There is a paucity of good animal models of gram-positive infection and a lack of microbiologic data from some of the major trials in sepsis that might have given greater insight into the mechanisms leading to shock in various infections.