The role of bacterial surface structures in pathogenesis

Modern research has revealed that the true surfaces of animal cells consist of polysaccharide chains that are linked to proteins hydrophobically anchored in the membrane and protrude to form a dense glycocalyx. It has become increasingly clear that most pathogenic bacteria must position themselves at the surface of their "target" cell in order to exert their toxic or otherwise deleterious effects. The true surface of most pathogenic bacteria has also been recently shown to consist of a protruding mass of polysaccharide chains--the bacterial glycocalyx--that is composed of teichoic acids in many gram-positive species and of acid polysaccharides in many gram-negative organisms. Through this bacterial glycocalyx certain cell surface proteins and organized protein structures (e.g., pili) are known to project, so that the bacterial surface is a mosaic of polysaccharides and proteins; both of these types of molecules have been implicated in instances of specific pathogenic adhesion. Besides their role in specific adhesion to target cells, these surface components interpose a highly charged, and often very extensive, barrier that can prevent the penetration of antibodies and antibiotics to their target sites in the bacterial cell. They may also frustrate mucociliary clearance, phagocytosis, and other clearance mechanisms of the host. We will discuss the chemical and physical nature of these bacterial surface components that mediate pathogenic adhesion and counteract host defense mechanisms sufficiently to allow infections to become established.