Models for studying the role of bacterial attachment in virulence and pathogenesis.

Simple in vitro tests for bacterial adhesion can indeed identify the various adhesive mechanisms of bacteria on an immunologic, physiochemical, biochemical, and genetic basis. Difficulties in interpretation arise, however, when attempts are made to relate the presence of a given adhesion to the colonizing ability or virulence of a bacterium. The reasons for this confusion are threefold: (1) there is more than one basic mechanism by which bacteria may associate with mucosae; (2) numerous intervening reactions in the mucosal microenvironment modify the various steps leading to association; and (3) mucosal association may sometimes be detrimental to a bacterium. Bacterial association with the mucosa, therefore, is determined by the final equilibrium established as a consequence of various synergistic and antagonistic reactions. An understanding of such a complex, interdependent system of reactions cannot be gained solely by studying each of its component parts in isolation. More complex models, such as those developed in experimental animals, are therefore required, and the relationship between adhesion and colonization must be explored within the conceptual framework employed by ecologists.