Adherence & colonization properties of Vibrio cholerae & diarrhoeagenic Escherichia coli

Bacterial adherence to host cells is the initial key step towards colonization and establishment of infection within the host. The adherence process requires the participation of two components: an 'adhesin' (adherence or colonization factor) of bacteria and a 'receptor' on the host (eucaryotic) cell surface. Many bacteria express several distinct and alternative mechanisms of cell adherence depending on the environmental conditions and nature of the adhesins as well as receptors. Bacteria causing gastrointestinal infection need to penetrate the mucous layer before attaching themselves to epithelial and other absorptive cells in the intestine. This attachment is usually mediated by fimbriae or pilus structures although other cell surface components of bacteria may also take part in the process. Adherent bacteria colonize intestinal epithelium by multiplication and initiation of a series of biochemical reactions inside the target cell through signal transduction mechanisms (with or without the help of toxins). Alternatively, adherent bacteria induce extensive rearrangement of the cytoskeletal structure of the epithelial cell thereby making more intimate contact with the cell or even forcing their entry into it. This is followed by bacterial multiplication and intercellular spread leading to eventual death of the target cell. Available information on the adherence and colonization properties of V. cholerae and E. coli, the two important causative agents of gastrointestinal illness in man, is discussed and summarized in this article.