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49 Cards in this Set

  • Front
  • Back
What is a pathogen?
-an organism that causes disease
-causes disease in healthy hosts
-causes disease in compromised host
What is pathogenicity?
-ability of organism to cause disease
-degree of pathogenicity
Where are virulence factors often found?
-on virulence plasmids or regions of chromosome called pathogenicity islands
What are Koch's Postulates?
1) suspected germ must be in every case of disease (and not in healthy ones)
2) the germ must be isolated and grown in pure culture
3) Cultured germ must cause disease when inoculated into a healthy, susceptible experimental host
4) Same germ must be reisolated from the diseased experimental host
What are some problems with Koch's postulates?
-assumes virulence is independent of host
-impossible to culture some disease-causing organisms
-polymicrobic infections
-cultivation can lead to loss of virulence factors
-ethics of intentionally infecting humans
What are polymicrobic infections?
-multiple microbes are necessary for pathogenesis
What are three things that lead to disease-causing infections?
-aggressive outsiders (primary pathogens)
-commensal microbes in wrong niche
-host is compromised, ecosystem balance disrupted
What are some portals of entry for pathogens?
-broken skin/bites
What are parenteral access points?
-broken skin
-insect bites
What are adhesins?
-ligands that bind to host cell receptors that can determine the specificity of infection of pathogen
What are some adhesin factors?
-glycocalyx/capsule/slime layer
-adherence proteins
-lipoteichoic acid
-fimbriae (pili)
What are extracellular enzymes?
-enzymes secreted by the pathogen
What is the purpose of extracellular enzymes?
-to dissolve structural chemicals in the body
-help pathogen maintain infection, incade and spread futher, and avoid body defenses
What do Hyaluronidase and collagenase do?
-degrade hyaluronic acid, a component of teh extracellular matrix, and collagen respectively
-S. aureus; staph infections
What do coagulase and kinases do?
-coagulase forms blood clots that provide a hiding place for microbes
-streptokinases and staphylokinases digest blood blots adn release microbes
*S. aureus, S. pyogenes
What digest blood clots to release microbes?
-streptokinases and staphylokinases
What are virulence toxins?
-chemicals or proteins produced by pathogen
-harm tissues or trigger host immune responses that cause damage
What are endotoxins?
-(lipid A): portion of outer membrane of G- bacteria released upon cell death or phagocytosis
-induce inflammation and immune responses that damage host cells
What are exotoxins?
-protein toxins released extracellularly by the growing pathogen that can travel and cause damage in distal sites; cytotoxin, neurotoxin, enterotoxin
Where can exotoxins act?
-act on cell surface; cytolytic by forming pores in membranes
-act on intracellular targets
What are some exotoxins formed from representative diseases.
-botulism, tetanus, gas gangrene, diptheria, cholera, plague, staphylococcal food poisoning
What are A-B toxins?
-composed of two protein subunits
-A is an enzyme, B is specificity subunit
-A enters cell through B OR with B
How does diphtheria toxin work?
-a subunit ADP-ribosylates elongation factor-2, shutting down protein synthesis
What are the four targets for extracellular toxins acting on intracellular toxins?
-protein synthesis
-signal transduction
-intracellular trafficking
What does tetanus toxin cause?
What does botulinum neurotoxins B, D, G, and F cause?
-spastic paralysis
-flaccid paralysis
What creates Botulinum toxin?
-Clostridium botulinum
How does Botulinum toxin work?
-blocks release of activating neurotransmitter acetylcholine
-inhibits components of the exocytosis machinery (VASP, SNAPs)
What does Botulinum toxin result in for muscles?
-inability of muscle to contract: flaccid paralysis
What produces Tetanus toxin?
-Clostridium tetani
How does tetanus toxin work?
-inhibits the release of inhibitory neurotransmitters
-inhibits components of the exocytosis machinery like botulinum toxin
What does tetanus toxin cause?
-rigis paralysis in face (lockjaw) adn then respiratory failure- spastic paralysis
-mortality rate very high
If infected with tetanus toxin, what can be done?
-tetanus antitoxin can be used to inhibit the toxin
-tetanus vaccine is very effective
What are enterotoxins?
-exotoxins that acts on the small intestine
-usually causes massive secretion of water into the intestinal lumen
What produces the Cholera toxin?
-Vibrio cholerae
Describe the Cholera toxin and how it works.
-A-B toxin; 1 A subunit and 5 B subunits
-Part of A subunit activates adenylate cyclase which makes cAMP, which stimulates cell to secrete Cl- and Na+, leading to water loss from cells
How do exotoxins work?
*Lipid A portion of LPS
-released into circulation when bacteria lyse
-activates complement which leads to inflammation
*cytokines released from Leukocytes
What do high concentrations of cytokines cause?
-activate immune system and leads to septic shock
What are some therapies for toxin-induced diseases?
-antitoxins; inhibit the action of the toxin
-toxoids; toxins inactivated by heat or chemical treatment (use as vaccines)
What are Type I toxins?
-toxins that inappropriately stimulate the immune system, leading to cell damage and toxic shock
What are three types of superantigens and what bacterium produce them?
-TSS toxin; S. aureus
-Streptococcal pyrogenic exotoxin; S. pyogenes
-Staphylococcal enterotoxin; S. aureus
What is TSS toxin responsible for?
-fever and other symptoms of toxic shock syndrome
What is Streptococcal pyrogenic oxotoxin responsible for?
-responsible for fever and other symptoms of toxic shock-like syndrome
What is Staphylococcal enterotoxin responsible for?
-stimulates vagus nerve
-leads to vomiting and other symptoms
What are antiphagocytic factors for?
What are two types of antiphagocytic factors?
-used to elude macrophages in the host immune system
-bacterial and fungal capsules, and antipahgocytic chemicals
Describe bacterial and fungal capsules.
-composed of polysaccharides found in body and not recognized by immune system
-slippery, making it difficult for phagocytes to engulf the bacteria
-Crytococcus neoformans
What is Crytococcus neoformans?
-a deadly fungus which has an antiphagocytic capsule
How do Antiphagocytic chemicals work?
What are two bacterium and what do they do?
-some prevent fusion of lysosome and phagocytic vesicles
-M proteins of S. pyogenes resist phagocytosis
-S. aureus makes leukocidins that directly destroy phagocytic white blood cells
What do the virulence factors of Salmonella cause?
-typhoid fever and salmonellosis (food poisoning)
Do pathogens have more than one virulence factor?
-YES! Very common to have multiple factors