[Microbial toxins].
Microbial toxins represent major virulence determinants of pathogenic bacteria. Endotoxins are lipopolysaccharides of the gram-negative bacterial cell wall. They exert their action via deregulating host cell function and stimulating cytokine overproduction. Exotoxins are proteins that can conveniently be grouped into three major categories. The first are intracellularly active molecules, all of which have to date been identified as enzymes. The second are membrane-damaging molecules, most of which create transmembrane pores. The third are the superantigens that cross-link T cells with antigen-presenting cells, thus causing cytokine overproduction. Most pathogens elaborate several toxins that can synergize in their detrimental action. Research on microbial toxins has fundamentally advanced our understanding of the pathogenesis of bacterial infections in the past two decades.