2.4

Question 1

What are the factors that influence the outcome of infection?

Answer 1

Agent infectivity
environmental pressure
host susceptibility

Question 2

What are the two main parts of the immune system?

Answer 2

innate immune system
- first line of defense
adaptive immune system
- B-cells and T-cells

Question 3

What happens when the binding of antibodies to antigens inactivates antigens?

Answer 3

1. neutralization
2. agglutination of microbes
3. precipitation of dissolved antigens
   
   • enhances phagocytosis
4. activation of complement system
   
   • leads to cell lysis

Question 4

What are proteases?

Answer 4

enzymes that break down proteins
- C-proteases: destroy complement proteins
- Ig proteases: destroy antibodies

Question 5

What are invasins?

Answer 5

rearrange host cell components to facilitate the movement of a microbe into a cell
- hyaluronidase: breaks down cell to cell adhesions
- collagenase: breaks down the protein collagen
- coagulase: converts fibrinogen to fibrin clot to isolate (can hid from immune system)
- kinases: break down fibrin

Question 6

Evasion of entry: streptococcus spp.

Answer 6

M-protein is strongly anti-phagocytic and destroys complement proteins

Question 7

Evasion of entry: neisseria spp.

Answer 7

capsule impairs phagocytosis by limiting the attachment of white blood cells
- glycocalyx

Question 8

evasion of entry: yersinia spp.

Answer 8

injects virulence factors via type III to prevent ingestion

Question 9

evasion of digestion: salmonella spp.

Answer 9

injects virulence factors via type III to prevent lysosome fusion with the phagosome

Question 10

evasion of digestion: mycobacteria spp.

Answer 10

waxes resist destruction by digestive enzymes

Question 11

evasion of digestion: shigella spp.

Answer 11

injects virulence factors via type III to escape the phagolysosome and spread to neighboring cells
- moves at last second

Question 12

What are the three ways pathogens can damage host cells?

Answer 12

1. use host nutrients depriving them of important factors
   ex. siderophores: stealing iron
   ex. tapeworms
2. cause structural or functional disruption at the site of infection
   ex. COVID-19 or S. pyogenes (necrotizing fascitis) causes DIRECT damage to tissue and cells
   ex. Rheumatic fever (S. pyogenes) or tuberculosis (M. tuberculosis) cause indirect damage to tissue, damage due to immune response
3. produce toxins
   - toxins are poisonous compounds that are produced within living cells, toxigenicity is the ability of a microbe to produce a toxin
   
   • endotoxin: lipid A, a toxin found within the cell, can lead to septic shock (gram-negative)
   • exotoxin: bacteria secretes exotoxin like cytotoxins, carried as genes on a plasmid and inhibit certain metabolic functions (gram-positive)
     ex. clostridium botulinum

Question 13

What is LD50?

Answer 13

median lethal dose for 50% of a sample population tested
- used to measure the potency of toxins

Question 14

What are membrane disrupting toxins?

Answer 14

a type of exotoxin
- cause lysis of cells by disrupting the membrane, common types are hemolysins (RBCs)
ex. streptococcus
- a hemolytic: green, partial hemolysis
- b hemolytic: clear, complete hemolysis
- y-hemolytic: no hemolysis
- causes lysis of cells disrupting the membrane, common types are leukocidins (WBCs)

Question 15

What are staphylococcus aureus toxins?

Answer 15

Both hemolysins and leukocidins

Question 16

What are A-B toxins?

Answer 16

two-component toxin including A component (active) and B component (binding)
ex. corynebacterium diphtheriae, diphtheria toxin inhibits RNA translation
ex. clostridium tetani, tetanus toxin inhibits fusion of vesicle containing inhibitor neurotransmitters
ex. clostridium botulinum, botulinum toxin inhibits fusion vesicles containing excitatory acetylcholine neurotransmitters

Question 17

How does the process of the diphtheria toxin work?

Answer 17

1. Diphtheria toxins receptor binding domain (B) binds host membrane
2. membrane-bound toxin (A+B) enters by endocytosis
3. catalytic subunit A is cleaved but held to the B subunit by disulfide bonds. Endosome vesicle acidifies, the disulfide bonds are reduced
4. the transmembrane domain facilitates passage of the catalytic A peptide through the vesicle membrane
5. the catalytic A domain ADP-ribosylates elongation factor 2 (EF2). This halts protein synthesis and kills the cell

Question 18

What are second-messenger toxins?

Answer 18

toxins that disrupt secondary messengers of cellular signal pathways (sub-class of A-B toxins)
ex. bacillus anthracis
ex. bordetella pertussis, pertussis toxin disrupts signaling pathways of immune system
ex. vibrio cholerae

Question 19

Bacillus anthracis

Answer 19

secondary messenger
anthrax toxin disrupts signaling pathways of the immune system

Question 20

Bordetella pertussis

Answer 20

secondary messenger
pertussis toxin disrupts signaling pathways of immune system

Question 21

vibrio cholerae

Answer 21

secondary messenger
cholera toxin disrupts intestinal osmotic balances resulting in rapid fluid floss

Question 22

Exiting the host

Answer 22

most pathogens are not adept to long-term survival within their host, making their escape from the host a necessity in order to find a new organism to invade
ex. vibrio cholerae, bacteria escapes by diarrhea
CVEC = conditionally viable environmental cells (cannot be cultured)