Flashcards in Part 7: Parthogenesis Deck (77):
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Infection
Growth of microbes that are not normally present in the host (regardless of whether or not the host is harmed)
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Disease
Damage or injury that impairs regular host functions
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Pathogen
A microbe that is able to cause disease
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Opportunistic pathogen
A microbe that causes disease only in the absence of normal host resistance
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Examples of opportunistic pathogens
Streptococcus pneumoniae and E. coli
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Streptococcus pneumoniae
Causes pneumonia in immunocompromised patients
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E. coli
Causes urinary tract infection when bacteria from feces are moved into the urethra
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Pathogenicity
The ability to cause disease
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Virulence
The severity of the disease that is caused - often given as an LD50 value
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LD50
Number of cells of a pathogen (or dose of a toxin) that will cause death in 50% of infected animals
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LD50 of Streptococcus pneumoniae
50 cells
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LD50 of Samonella enterica
5000 cells
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Pathogenesis
The process by which a disease develops
Steps that lead to an infection and tissue damage
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Virulence factors
Genetically encoded traits that contribute to a pathogen's ability to cause disease
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Adherence
Ability for a pathogen to stick to a surface and begin colonization
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Non-covalent adherence example
Capsules and slime layers
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Streptococcus mutans non-covalent adherence factors
Uses slime layer to stick to teeth and form a biofilm
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Streptococcus pneumoniae non-covalent adherence factors
Uses capsule to stick to cells in the lungs
Also protects the cell from phagocytes
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Adhesins
Specific surface molecules that allow selective adherence to particular cell types
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Enterotoxigenic E. coli adherence factors
Produce fimbriae and can adhere specifically to cells in the small intestine
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Neisseria gonorrhoeae produces what adherence factors
Fimbriae that allow it to attach to mucosal epithelial cells - retract to bring bacteria close to the membrane
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Opa proteins
Specifically attach to certain receptors on the host cell
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Invasiveness
The ability of a pathogen to enter into host cells or spread through tissues
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Virulence factors that promote invasiveness
Siderophores, exoenzymes, invasins
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Siderophores
Iron binding molecules
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Siderophore mechanism
Host proteins transferrin and lactoferrin - sequester iron, making it unavailable for other microorganisms - limits the growth of invaiders
Siderophores rip iron out of tissues to be used by bacteria
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Types of exoenzymes
Hyaluronidase
Collagenase
Proteases, nucleases, and lipases
Fibrinolysin
Coagulase
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Hyaluronidase
Hydrolyzes hyaluronic acid (cement that holds animal cells together)
Allows pathogen to spread between cell
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Collagenase
Degrades collagen
Allows pathogen to spread through tissues
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Proteases, nucleases, and lipases
Degrade host macromolecules
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Fibrnolysin
Dissolves fibrin clots
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Example of fibrinolysin
Streptococcus pyogenes makes streptokinase
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Coagulase
Induces fibrin clots
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Example of coagulase
Staphylococcus aureus produces coagulase to protect it from phagocytes
Keeps staph infections localized
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Invasins
Proteins that allow bacteria to invade and enter directly into host cells
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Listeria monocytogenes
Non-lactic acid, non-spore forming psychrotolerant member of Firmicutes
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Where is Listeria monocytogenes found?
Unpasteurized dairy products, improperly packaged processed meats
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Listeria monocytogenes produce
Invasins that promote phagocytosis by macrophages
Hijacks the cytoskeleton to escape the phagolysosome
Spreads from cell to cell
Avoiding humoral immune response
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Bacteremia
Bacteria in the blood
Can be carried to different organs and tissues
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Septicemia
Bacteria multiplying in the blood (i.e., a blood borne systemic infection)
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Septicemia can lead to
Sepsis - widespread systemic inflammation
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Septic shock is caused by
Gram negative bacteria, gram positives: staphylococci and enterococci
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Exotoxins
Proteins released by growing bacteria that inhibit host cell function (or kill host cells), usually heat labile, can be extremely toxic
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Bacillus anthracis virulence factors
Capsules, exoenzymes, and the anthrax toxin
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Anthrax toxin
Interferes with the immune response and kills macrophages
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Categories of exotoxins
Cytoxins, AB toxins, superantigens
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Cytoxins
Disrupt cytoplasmic membrane integrity - cell lysis and death
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Examples of cytotoxins
Hemolysins, lecithinase or phospholipase, and leukocidins
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Hemolysins
Lyse many cells (not just red blood cells)
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What produces hemolysins?
Streptococcus pyogenes
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Streptococcus pyogenes produces
Streptolysin
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Streptolysin
Attacks sterols in the cell membrane
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Lecithinase or phospholipase
Dissolves membrane lipids
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Example of lecithinase or phospholipase
Clostridium perfringens - alpha toxin (gas gangrene)
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Leukocidins
Destroy white blood cells
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Example of leukocidins
Staphylococcus aureus - staphyloccal alpha toxin
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Leukocidin mechanism
Toxin subunits insert into the membrane and oligomerize to form a heptamer
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Heptamer
A membrane spanning pore
Cell contents leak out and the cell dies
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AB toxin is made of
Active subunit and binding subunit
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Example of AB toxin
Diphtheria toxin
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What produces diphtheria toxin?
Corynebacterium diphtheriae
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Diphtheria toxin mechanism
Subunit B - specifically binds to a protein on animal cells
Subunit A - then moves across the membrane (interferes with protein synthesis)
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Where is the gene for the diphtheria toxin?
On a virus, not on the chromosome
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Other AB toxin
Tetanus, botulism, and cholera toxins
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Super antigens
Activate T-cells to elicit an extreme immune response
Bind to MHC molecules TCRs outside the antigen binding site
Bridge the gap and mimic proper antigen
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What do superantigens activate?
Huge number of T cells
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T cells produce
Cytokines
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Cytokine reaction
Extreme immune response
Extreme fever, systemic inflammation, shock, death
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Example of superantigen
Staphylococcus aureus' toxin shock syndrome toxin
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Endotoxins
Lipopolysaccharide from the Gram negative outer membrane
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Toxic part of endotoxin
Lipid A
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Lipid A is released
When cells die
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Which is more toxic: exotoxin or endotoxin
Exotoxins
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Example of endotoxin
Samonellosis
Gram negative sepsis
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Samonellosis mechanism
Colonizes the intestine - multiply to a huge number of bacteria
As bacteria die, they release endotoxin
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Symptoms of Samonella
Fever, diarrhea, generalized inflammation
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