Pili

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

Pili are responsible for haemagglutination in bacteria and also for intercellular adhesiveness giving rise to clumping. At present, a clear role for these structures has not been formulated. 

F-pili or sex strands are partofa primitive genetic exchange system in some bacterial species. Part of the genetic material may be passed from one cell to another through the hollow pilus, thus giving rise to a simple form of sexual reproduction. 

Not all oxidants formed biolc cally have the potential to promote lipid peroxidation. The free radicals superoxide and nitric oxide [or endothelium-derived relaxing aor (EDRF)] are known to be formed in ww but are not able to initiate the peroxidation of lipids (Moncada et tU., 1991). The protonated form of the superoxide radical, the hydroperoxy radical, is capable of initiating lipid peroxidation but its low pili of 4.5 effectively precludes a major contribution under most physiological conditions, although this has been suggested (Aikens and Dix, 1991). Interestingly, the reaction product between nitric oxide and superoxide forms the powerful oxidant peroxynitrite (Equation 2.6) at a rate that is essentially difiiision controlled (Beckman eta/., 1990 Huie and Padmaja, 1993). 

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

S. J. Vesper, Production of pili (fimbriae) by Pseudomonmas fluorescens and correlation with attachment to corn roots. Applied and Environmental Microbiology 53 1397 (1987). 

In general, virus receptors carry out normal functions in the cell. For example, in bacteria some phage receptors are pili or flagella, others are cell-envelope components, and others are transport binding proteins. The receptor for influenza vims is a glycoprotein found on red blood cells and on cells of the mucous membrane of susceptible animals, whereas the receptor site of poliovirus is a lipoprotein. However, many animal and plant viruses do not have specific attachment sites at all and the vims enters passively as a result of phagocytosis or some other endocytotic process. 

A number of bacterial viruses have RNA genomes. The best-known bacterial RNA viruses have single-stranded RNA. Interestingly, the bacterial RNA viruses known in the enteric bacteria group infect only bacterial cells which behave as gene donors (males) in genetic recombination. This restriction to male bacterial cells arises because these viruses infect bacteria by attaching to male-specific pili. Since such pili are absent on female cells, these RNA viruses are unable to attach to the females, and hence do not initiate infection in females. 

In Gram-negative bacteria which are characterised by a rather complex cell envelope, the CM is also referred to as inner membrane to distinguish it from a second lipid bilayer, termed outer membrane (OM). The space between these two layers is called the periplasm (PP). In the periplasmic space, many proteins are found with a variety of functions. Some are involved in biosynthesis and/or export of cell wall components and surface structures (e.g. pili, flagellae,... 

Plasmids and DNA Repair. Plasmids are extrachromosomal genetic elements that are composed of circular double-stranded DNA. In bacteria some can mediate their own transfer from cell to cell by conjugation they contain a set of Ira genes coding for tube-like structures, such as pili, through which a copy of plasmid DNA can pass during transfer. Plasmids range in size from 1.5 to 200 million daltons. The number... 

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. 

Allen-Vercoe, E., Waddell, B., Livingstone, S., Deans, J., and DeVinney, R. (2006). Entero-pathogenic Escherichia coli Tir translocation and pedestal formation requires membrane cholesterol in the absence of bundle-forming pili. Cell. Microbiol. 8, 613-624. 

Cleary, J., Lai, L.-C., Shaw, R. K., Straatman-lwanowska, A., Donnenberg, M. S., Frankel, G., and Knutton, S. (2004). Enteropathogenic Escherichia coli (EPEC) adhesion to intestinal epithelial cells Role of bundle-forming pili (BFP), EspA filaments, and intimin. Microbiology 150, 527-538. 

Dean, E. A. (1990). Comparison of receptors for 987P pili of enterotoxigenic Escherichia coli in the small intestine of neonatal and older pig. Infect. Immun. 58, 4030-4035. 

Kuehn, M. J., Heuser, J., Normark, S., and Hultgren, S. J. (1992). P pili in uropathogenic E. coli are composite fibres with distinct fibrillar adhesive tips. Nature 356, 252-255. 

Tobe, T., and Saskawa, C. (2002). Species-specific cell adhesion of enteropathogenic Escherichia coli is mediated by type IV bundle-forming pili. Cell. Microbiol. 4, 29M2. 

Xicohtencatl-Cortes, J., Monteiro-Neto, V., Ledesma, M. A., Jordan, D. M., Francetic, O., Kaper, J. B., Puente, J. L., and Giron, J. A. (2007). Intestinal adherence associated with type IV pili of enterohemorrhagic Escherichia coli 0157 H7. /. Clin. Invest. 117,3519-3529. 

FIGURE 3.7 Elements of mammalian skin glands. S, sebaceous gland A, apocrine gland E, eccrine gland M, errector pili muscle H, hair follicle. (From Albone, 1984.)... 

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