Fimbriae, bacterial

The initial adherence of pathogens to host cell surfaces is considered an essential step in colonization and infection (Savage, 1977, 1984). Therefore, identifying the bacterial molecules that mediate adherence has been a major area of research, especially since these molecules may serve as targets for anfi-adherence strategies. As discussed previously (Section VI), the detailed interactions between a pathogen and a host cell are often mediated by proteinaceous surface structures on the bacterial surface. These bacterial proteins are referred to as adhesins (Finlay and Falkow, 1989), and are most often foimd on the tips of bacterial fimbriae or pili (fimbrial adhesins), but may also be anchored in the bacterial membrane so that it can be presented on the bacterial outer membrane (afimbrial adhesins) (Sharon and Ofek, 1986). Models of fimbrial and afimbrial adhesins of some human pathogens are discussed here. 

Bacteria causing gastrointestinal infection need to penetrate the mucus layer before attaching themselves to the epithelial surface. This attachment is usually mediated by bacterial fimbriae or pilus structures, although other cell surface components 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) (51). 

The terminal disaccharide of the ceramide trihexoside isol. from normal human kidney and erythrocytes a dcgradn. prod, of mucilage from common okra (Hibiscus esculentus) formed by the action of P-galactosidase on i>galactose The simplest structural unit capable of bacterial fimbriae binding associated with initiation of bacterial infections. Cryst. (MeOH/ l-butanol/H20). 

Fig. 24.1 (a) A mixed popuiation of bacteria with substantiai attachment of pathogenic bacteria, (b) Competitive exciusion of pathogens due to preferential attachment of non-pathogens. It should be noted that the recognition of receptor sites (carbohydrates) by the bacterial fimbriae (lectins) is very specific to different types of organism. 

Pangbum, M.K. Activation of Complement via the Alternative Pathway , Federation Proceedings (1983), 42, 139-42 Pearce, W.A. and Buchanan, T.M. Structure and cell-membrane-binding properties of bacterial fimbriae In E. H. Beachey (ed.). Bacterial ASierence (Academic Press, London, 1980) pp. 289-344 Smith, H. Microbial Surfaces in Relation to Pathogenicity , Bacteriological Reviews (1977), 41, 475-500... 

Three types of thread-like appendages may be found growing from bacterial cells flagella, pili (fimbriae) and F-pili (sex strands). 

A. Bacterial appendages (pili. fimbriae) Pseudomonas fluorescens 86... 

In addition to flagella, extremely thin, long, straight filaments known as pili or fimbriae (Fig. 1-2) project from the surfaces of many bacteria.14 The "sex pili" (F pili and I pili) of E. coli have a specific role in sexual conjugation. The similar but more numerous common pili or fimbriae range in thickness from 3 to 25 nm and in length from 0.2 to 2 pm. Pili are involved in adhesion of bacteria to surrounding materials or to other bacteria and facilitate bacterial infections.17-19 A typical E. coli cell has 100-300 pili.5... 

Microbial pathogens utilize different types of lectins for targeting the glycans on the surface of host cells. Many bacteria are covered with pili or fimbriae that contain a very special class of lectins known as adhesins because they play a role in attachment to epithelial cells. These lectins are monomeric and comprise only one binding site. Because the adhesins are repeated on the pilus, a larger number of adhesins on the bacterial surface create multivalent interaction with the host glycans. 

Pallesen L, Poulsen LK, Christiansen G, Klemm P, Chimeric. FimH. Adhesion, of type 1 fimbriae A bacterial surface display system for heterologous sequences, Microbiology, 141 2839-2848, 1995. 

Moreover, Sharon (72) has already demonstrated that bacterial lectins at the tip of fimbriae possess subtle but different affinities for aromatic a-D-mannopyranosides, thus illustrating the effect of what we coined sub-site-assisted aglycone binding (75). For instance, a-D-mannopyranosides 2-4 (Scheme 1) showed 69 to 1015-fold increased inhibitory properties in comparison to methyl mannoside 1 (72). Additionally, discrete differences can be observed between the inhibitory properties of a given mannoside derivative against different strains of bacteria, thus illustrating again that selectivity can be achieved. 

Bacteria are simple unicellular organisms that constantly grow. They have a membrane and cell wall. Fimbriae are especially important for bacterial adhesion, a critical factor in dental disease development. Lipopolysaccharide is a covalent lipid and polysaccharide structure that contains unusual saccharides and fatty acids. The lipid is at one end and inserts it into the plasma membrane. LPS is invariably recognized as foreign by receptors on mammalian cells that recognize the unique structure and activate inflammation such as gingivitis. 

Acellular pertussis vaccines contain selective components of the B. pertussis organism. All acellular vaccines contain pertussis toxin (PT), and some contain one or more additional bacterial components (e.g., filamentous hemagglutinin [FHA], pertactin [a 69-kDa outer membrane protein], and fimbriae types 2 and 3). Acellular pertussis vaccine is recommended for all doses of the pertussis schedule at 2, 4, 6, and 15 to 18 months of age. A fifth dose of permssis vaccine is given to children 4 to 6 years of age. Pertussis vaccine is administered in combination with diphtheria and tetanus (DTaP). Although the permssis vaccine is not recommended for individuals 7 years of age and older, booster doses for adolescents and adults may be incorporated into future recommendations because members of these groups are important reservoirs of infection. 

---