Structure, composition and functions of surface structures on oral bacteria

Abstract

This review describes the surface structures (fibrils and fimbriae), on oral bacteria that can be responsible for adhesion to buccal mucosa, teeth and other bacteria (coaggregation). Fibrils and fimbriae have been found on a number of different species of Streptococcus, Actinomyces and Bacteroides, and are morphologically and biochemically distinct from each other. Either structure can be present on different strains of the same species of Streptococcus. Fibrils or fimbriae are present on different species of Bacteroides, and Actinomyces species only exhibit fimbriae. The evidence for the existence of two distinct types of surface structure is evaluated. Fimbriae are flexible peritrichous structures composed of protein, with sub‐unit molecular weights varying from 43 kDa for Bacteroides gingivalis 381 fimbriae, to 65 kDa for Actinomyces viscosus T14V fimbriae. Fimbriae are thin (3–5 nm wide) and are characterised by a definite width all along their length. Fibrils can be either peritrichous, or less commonly arranged in lateral tufts, and they have a reproducible length (Streptococcus salivarius HB, to 320 kDa for the fibrillar veillonella binding protein, also from S. salivarius HB. Some fibrils and fimbriae carry multiple adhesins adhering to more than one type of receptor. The evidence linking fibrils and fimbriae with adhesion to oral surfaces is assessed.