Exam 3 Lecture 25

Question 1

Falkow’s Molecular Koch’s Postulates

Answer 1

1. phenotype must be associated with pathogenic strain
2. specific inactivation should lead to loss in virulence
3. replacement of the mutated gene should restore pathogenicity

(this is kind of like find it lose it rescue)

Question 2

Mechanisms of bacterial pathogenesis:

Answer 2

1. production of toxins
2. attaching and colonizing a host surface
3. invasion of host tissues
4. avoiding host defenses

Question 3

exotoxin

Answer 3

protein toxins

Question 4

What does a pore-forming toxin do?

Answer 4

Oligomerizes in the host cell membrane and forms a pore that allows cytoplasmic contents to leak out

Question 5

pore forming toxin mechanism?

Answer 5

First present as inactive monomers in solution. When they bind to protein or lipid receptor, they recruit other monomers and this forms a pore. Or a preformed oligomer can just insert into the membrane.

Question 6

What is Pore Forming Toxin structure in the membrane?

Answer 6

Forms beta barrel, 7 monomers

Question 7

What is AB exotoxin?

Answer 7

A is the toxin, B is the binding portion that will bind to receptor

Question 8

What kind of activity does A have of AB toxin?

Answer 8

ADP ribosyltransferase activity. Depending on the target protein, this transfer can either inactivate or constitutively express

Question 9

Cholera toxin mechanism

Answer 9

AB toxin binds to receptor, A enters cell and locks G protein in on position, turning on adenylate cyclase, increases cAMP concrentation, causes ion channels to open and release ions out of cell, water follows due to osmosis

Question 10

How can bacteria adhere to cell surfaces?

Answer 10

Express adhesins, such as pili, cell surface proteins, capsules

Question 11

True or false: bacteria can adhere to any type of cell to cause infection

Answer 11

False. The adherence is cell type specific and hijack certain hsot receptors. This causes localized infections

Question 12

impediments to colonization

Answer 12

compete with host microbiome; obtain nutrients; mucosal immunity

Question 13

____ is the most limiting nutrient during infection

Answer 13

Iron

Question 14

What proteins do the host make to prevent iron toxicity?

Answer 14

lactoferrin, transferrin, hemoglobin

Question 15

Siderophores

Answer 15

Small molecules that bind to iron very tightly that can then be used by bacteria

Question 16

Main antibody present at mucosal surface

Answer 16

Secretory IgA (secreted by plasma cells)

Question 17

How can bacteria protect against secretory IgA?

Answer 17

capsule, secrete protease to cleave IgA, antigenic variation (changes type of surface protein expressed)

Question 18

examples of invading host tissue

Answer 18

through damaged skin, maybe even hair follicle, through mucous membrane (entry through damaged epithelium, or forced invasion)

Question 19

Salmonella invasion mechanism

Answer 19

TYPE 3 Secretion System!!!

Uses injectosome to “inject” effector molecules

Question 20

What do effector molecules?

Answer 20

cause dramatic rearrangement of host cytoskeleton. this can cause engulfing of the bacteria to force its way in

Question 21

M cell

Answer 21

samples environment in intestinal lumen, passes on these to macrophages on basolateral side of M cell

Question 22

How does shigella avoid M cell/macrophage?

Answer 22

It can survive inside a macrophage, then goes back into intestinal cells to protect itself (hides)

Question 23

Examples of phagocytes

Answer 23

Neutrophils, macrophages, dendritic cells

Question 24

How can bacteria avoid being killed by phagocytes?

Answer 24

prevent phagocytosis; survive inside phagocytes

Question 25

Opsonization

Answer 25

Bacteria is covered with antibodies to attract a phagocyte

Question 26

How can S. aureus prevent phagocytosis?

Answer 26

Has an Fc receptor that binds antibodies that face the wrong way. Fab regions will not be recognizable to macrophage (as it is not foreign), thus will not be engulfed

Question 27

Host cell mimicry

Answer 27

Bacteria can have hyaluronic acid capsule to appear non-foreign to host

Question 28

How does Listeria monocytogenes survive insside phagocyte?

Answer 28

engulfed into phagosome but secretes pore forming toxin (14 monomers) called LLO, allows bacterium to escape phagosome within 5 min before lysozyme fuses