Adhesins afimbrial

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. 

Fimbrial adhesins may be visualized by electron microscopy. However, the processing for analysis by electron microscopy might cause alterations of the specimens, e.g. by dehydration. This might result in the collapse of certain fimbriae. Therefore, despite no fimbriae are visible by electron microscopy the afimbrial adhesins of the Dr family, e.g. AfaE of diarrheagenic and uropathogenic E. coli in fact assemble... 

Other adhesins of E. coli as antigen 43, AIDA-I, TibA and intimin of enter-opathogenic and enterohemorrhagic E. coli are true afimbrial adhesins i.e. they are integral outer membrane proteins. However, also intimin seems to be involved in invasion of host cells [62, 63], Intimin, which is actually a whole family of adhesins, is the only example of an adhesion that uses a protein (Tir translocated intimin receptor) in the host cell membrane, that is a bacterial protein inserted into the host by the bacterial type 3 protein secretion system [64],... 

Besides fimbrial and afimbrial adhesins, there are other surface structures that act as adhesins. For example, in Pseudomonas aeruginosa the major flagellar protein flagellin was identified as the adhesin responsible for binding to Muc 1 mucin [67],... 

Garcia, M. 1., Gounon, P., Courcoux, P., Labigne, A., and Le Bouguenec, C. (1996). The afimbrial adhesive sheath encoded by the afa-3 gene cluster of pathogenic Escherichia coli is composed of two adhesins. Mol. Microbiol. 19, 683-693. 

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