Definition
Adhesion in microbiology is the ability of a cell or virus to attach to a surface, host tissue or another microorganism. It is often the first step in colonisation and infection.
Explanation
Microbial attachment depends on surface molecules called adhesins. Bacteria use pili, fimbriae and outer membrane proteins to recognise specific receptors on host cells. Some species secrete exopolysaccharides that glue cells to surfaces and to each other. Environmental conditions such as pH, moisture and surface roughness can influence attachment. Once a bacterium adheres it may trigger signalling pathways in the host and begin to grow as a biofilm. Fungi attach using mannoproteins and hydrophobins, while viruses use capsid proteins or envelope glycoproteins to bind to host receptors. Parasites like helminths have hooks and suckers that anchor them to intestinal walls. Adhesion is not accidental; it is a finely tuned interaction between microbial ligands and host receptors.
Examples and Impact
Pathogenic Escherichia coli express P fimbriae that attach to uroepithelial cells and cause urinary tract infections. Streptococcus mutans uses glucan‑binding proteins to adhere to teeth and form dental plaque. Candida albicans expresses agglutinin‑like sequence proteins that attach to mucosal surfaces. Viral examples include influenza haemagglutinin binding to sialic acid. By anchoring themselves microbes resist flushing forces and immune clearance. Anti‑adhesive strategies such as receptor analogues and surface coatings are being explored to prevent infections and biofouling.
Adhesion is a central feature of microbial ecology and disease. Understanding the molecules involved offers targets for therapies and helps explain how organisms colonise diverse environments.
Related Terms: Adhesins, Biofilm, Pili, Fimbriae, Virulence