Part 7: Parthogenesis Flashcards Preview

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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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Gram negative sepsis

Gram negative bacteria multiply in the blood
Killed by immune system, releasing endotoxin
Massive inflammation leads to septic shock and death