Multiple adhesins of streptococci

In summary, the multiple streptococcal adhesins appear to contribute to the overall ability of the organisms to colonize various niches in the upper respiratory tract. They do so by two modes. One involves two distinct adhesive steps, the first of which is readily reversible and requisite in order to pass to the second step, after which adhesion is essentially irreversible. The other depends upon the expression of one or more adhesins that may undergo phase variation, similar to the expression of mannose- sensitive and mannose-resistant adhesins by members of the Enterobacteriaceae (27, 32). It is recognized that the model proposed for streptococcal adhesion does not necessarily resolve all of the issues involved in this complex phenomenon, even for S. sanguis and S. pyogenes. The model does, however, provide an explanation for many observations of adhesion of these species that otherwise are difficult to resolve. Further understanding of adhesion mechanisms must take into account both strain and substratum variation and is not likely to result from simplistic analyses of biochemical or molecular genetic experiments alone. The model also permits the design of experiments needed to delineate further the various activities of multiple adhesins expressed by pathogenic streptococci.