BIO 315 Lecture Notes - Lecture 7: Lipoteichoic Acid, Lipopolysaccharide, Neisseria
13 Jun 2018
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Lecture 7: Bacterial Pathogenesis
Introduction
• Pathogenesis: the process used by pathogens to produce disease
• Key aspects:
• Attach to the host tissue and gain access
• Damage tissues to obtain nutrients and replicate
• Avoid host defense
• Genetic mobility is a principal feature in pathogen evolution
• Plasmids carry genes that allow pathogenesis
• Coesal: ateria preset i our ody that do’t ause har
Bacterial Virulence Factors
• Virulence factors: pathogen products that enhance their ability to cause disease
• Ex: Neisseria gonorrhoeae causes gonorrhea and the virulence factor fimbriae attaches to
the urethral or cervical epithelial tissues and the endotoxin LOS evokes inflammatory
damage
• Attachment factors
• Some of the first virulence factors a host will encounter are those the pathogen uses to
attach
• Fimbriae= specialized pili with an adhesive tip
o The tip protein binds to a specific receptor on a host cell
o Acts as a "probe" to get beyond the repulsing negative charge on the host cell
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o Can be altered by some microbes to evade immunity
▪ The expression of fimbriae can be turned off
• Bacterial toxins
• Endotoxins are a part of the cell wall structure and induce inflammatory responses
o LPS on the Gram-negative cells
o Lipoteichoic acid (LTA) on the Gram-positive cells
• Exotoxins are released outside the producing cell
o A-B toxins: B subunit binds to the host cell receptor; A subunit has a negative action
inside the cell
▪ A subunit stays the same but the size and amount of B subunit can vary
o Cytotoxins: toxins that directly act on host cells
▪ Cytolysins: act on plasma membrane
o Super-antigens: nonspecifically stimulate T cells to secrete large amounts of cytokines
Endotoxin and Lipoteichoic Acid
• LPS is the most common endotoxin
• It has three parts:
• O-antigen: often strain-specific and can be used for serotyping (method that uses antibodies
made to these substances for identifying closely related strains that differ in their surface
antigens)
o Composed of repeating units of polysaccharide
o Target of immune response
• Core polysaccharide
o Various sugars with side chains
o Genus or species-specific
• Lipid A: the inflammatory inducing portion
o Innermost component
o Hydrophobic nature allows it to anchor the LPS to the outer membrane
find more resources at oneclass.com
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Document Summary
Some of the first virulence factors a host will encounter are those the pathogen uses to attach. Innermost component: hydrophobic nature allows it to anchor the lps to the outer membrane, responsible for the toxicity, unusual fatty acids. Exotoxins: bacterial toxins: a-b toxins, b portion binds to a receptor on a host cell, a portion has enzymatic activity inside host cells, many pathogens secrete a-b. Shiga toxins: a-b toxins: e. coli, ribosomal rna cleavage prohibiting protein synthesis, pertussis toxin: a-b toxins, activates gi protein which activates adenylate cyclase; over-production of camp causes water and ion imbalance. Snare proteins in the host cells are used to release neurotransmitters. Lps interacts with cd14 cells and exotoxins interact with cd4 cells: each is capable of inducing inflammation individually. Inducing random inflammation confuses coordination of immune responses that would work to eliminate pathogens: together, they can act synergistically and induce shock and death. It possesses numerous virulence factors: removing one fa(cid:272)tor does(cid:374)"t preve(cid:374)t pathoge(cid:374)i(cid:272)ity.
