LM14 - Overviewofpathogenesis...

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Overview of pathogenesis • Pathogenesis: Process of how infections develop • Exposure to pathogens: coughing, sneezing, vectors  (e.g., insects), fomites (pathogens on inanimate  surfaces), injury • Adherence of pathogen to tissues: Slime layer, pili,  adhesion molecules • Colonization: Factors that allow pathogen to evade  immune system, grow within host • Escape: exit strategies 1
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Virulence • Virulence is the relative ability of a pathogen to  cause disease • Virulence depends on presence of cell structures  and/or production of toxins or other extra-cellular  proteins called virulence factors • Virulence factor genes found on plasmids,  lysogenic phage, and separately on chromosomes,  i.e., can be transferred horizontally • Virulence factors related to cell structures include  flagellae, pili, cell membrane (LPS), capsule, OMVs  (outer membrane vesicles) • Biofilms are formed by a combination of slime and  other adhesive molecules 2
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Pili (Fig. 30.3)  • (a) Some strains of  E. coli  have specialized fimbiae called  colonization factor antigens (CFAs) that allow them to  adhere to  intestinal cells, colonize and produce disease  Neisseria gonorrhoeae, Neisseria menigitides  have many  pilin gene segments for different pili that they change to  evade immune response; they use pili to adhere to  urogenital or upper respiratory epithelial cells (b) Vibrio cholerae  -- fimbriae key to colonization/infection • (c)  Candida albicans  also produces fimbriae for adhesion to  epithelial cells 3
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Capsules/slime (Figs.  3.31,21.17)  • Capsules usually composed of high Mol.Wt. polysaccharide  or amino acids ( B. anthracis  ) and help microbes evade 
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LM14 - Overviewofpathogenesis...

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