Stick to your gums: mechanisms of oral microbial adherence

Abstract

Studies on the adherence properties of oral bacteria have been a major focus in microbiology research for several decades. The ability of bacteria to adhere to the variety of surfaces present in the oral cavity, and to become integrated within the resident microbial communities, confers growth and survival properties. Molecular analyses have revealed several families of Gram-positive bacterial surface proteins, including serine-rich repeat, antigen I/II, and pilus families, that mediate adherence to a variety of salivary and oral bacterial receptors. In Gram-negative bacteria, pili, auto-transporters, and extracellular matrix-binding proteins provide components for host tissue recognition and building of complex microbial communities. Future studies will reveal in greater detail the binding pockets for these adhesin families and their receptors. This information will be crucial for the development of new inhibitors or vaccines that target the functional regions of bacterial proteins that are involved in colonization and pathogenesis.

Figure 1.

Diagrammatic representation of interactions occurring between oral micro-organisms and with host tissues that contribute to the formation of microbial communities within the human oral cavity. Microbial adhesins are represented as suction cups on stalks that may be flexible (e.g., pilus), while pellicle receptors are represented as molecular spheres. The adhesins are labeled according to the nomenclature in Table 1. Polysaccharides (RPS and glucan) are indicated as surrounding Streptococcus cells. Glucan-binding proteins (GBP) are not included in Table 1, although these play a crucial role in conjunction with glucosyltransferases (GTFs) in S. mutans colonization (Koo et al., 2010).

Figure 2.

Role of Fusobacterium nucleatum as a bridge between early- and late-colonizers. (A) F. nucleatum (orange) co-aggregates with many different genera, including early-colonizers such as streptococci (green), and with late-colonizers such as A. actinomycetemcomitans (purple) or T. denticola (blue). (B) Analysis of subgingival biofilms by fluorescence in situ hybridization with a specific probe for F. nucleatum (orange) shows that it is localized in the middle layer of the biofilm, between early- and late-colonizers (eubacterial probe; green). (C) The localization of F. nucleatum within the biofilm is highlighted in a cartoon depiction of panel B. Scale bar on panel B is 10 µm. Image B is adapted from Zijnge et al. (2010) with permission.