Bacterial cell fimbriae/pili

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

Virtually all bacterial species and genera express lectins or lectin-like activities, frequently of more than one type and with different specificities. However, it is usually not known whether individual cells coexpress multiple types of lectin or each lectin is confined to a distinct cell population. Many Gram negative bacteria (for example, Escherichia coli and Salmonellae spp.) and a few Gram positive ones (e.g. certain actinomyces), produce surface lectins that are often in the form of submicroscopic hairlike appendages known as fimbriae (pili) that protrude from the surface of the cells. The best characterized bacterial surface lectins with respect to their molecular properties, carbohydrate specificity and genetics are the type 1 fimbriae specific for mannose and the type P fimbriae specific for galabiose, [Gal(al-4)Gal], produced by many strains of E. coli. Other examples are S fimbriae of E. coli, specific for NeuAc(a2-3)Gal, and type 2... 

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. 

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. 

The surface of cells of some bacterial species is covered with many (10 to several thousands), thin (3-25 nm), and long (up to 12 pm) threads called pili, or fimbriae. They play a role in the initial adhesimi of bacteria to host tissues and inanimate surfaces [43, 44]. Attachment to a surface is the first step in biofilm formation. Upon attachment on tissue cells they may trigger a number of biochemical signals fi om the host, which ultimately leads to the bacterial disease [45]. 

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