8-2: Microbial Pathogenesis

Question 1

Which domain of life lacks pathogenic organisms?

Answer 1

Archaea! (or at least, we don’t know any yet)

Question 2

What are phytopathogens?

Answer 2

Microbial pathogens that target plants. Eg. Erwinia amylovora which targets apples.

Question 3

What are more common than bacterial pathogens targeting plants?

Answer 3

Fungal pathogens, eg. fusarium oxysporum, causing Panama disease in the Gros Michel bana

Question 4

What is Dutch Elm Disease>

Answer 4

Fungal pathogen carried by bark beetles from asia.

Question 5

What is an infection

Answer 5

Invasion of body by a disease-causing organism. Can result in disease, but not the same thing as disease.

Question 6

What is a disease

Answer 6

Damage or injury to host organism. Some bacteria cause disease without infection (using toxins).

Question 7

What is a pathogen

Answer 7

An organism that causes disease

Question 8

What is pathogenesis

Answer 8

Mechanism that leads to disease

Question 9

What is virulence

Answer 9

Similar to pathogenesis, used to describe the severity of the disease. Eg. “highly virulent”

Question 10

What is an opportunistic pathogen

Answer 10

Organism that is often non-pathogenic, but becomes pathogen under certain circumstances

Question 11

What are symptoms of a bacterial disease are caused by?

Answer 11

Activities of pathogen (eg. toxins, tissue damage) or immune response to pathogens (fever, rashes, redness, swelling)

Question 12

What are the 4 major steps in many infections/microbial diseases?

Answer 12

Adherence: binding to specific host cells/tissues
Colonization: expanding population (planktonic or biofilm)
Invasion: gain access to privileged sites through mucous membranes
Spread: move beyond site of initial infection

Question 13

What is a mucous membrane

Answer 13

Tightly packed epithelial cell layers covered with a protective mucous layer. Lines body access points (airways, oral cavity and GI).

Question 14

What is invasion

Answer 14

Ability of pathogen to enter host cells and/or tissues. Penetrate beyond where microbes usually reside

Question 15

Strategies of invasion

Answer 15

Entering host cells, damaging epithelial layers

Question 16

How does S. pyogenes invade cells?

Answer 16

Secreting enzyme called hyluranidase that degrades hyluronic acid, disrupting the epithelial layer.

Question 17

What is a virulence factor

Answer 17

Molecules produced by a pathogen that contribute to its ability to cause disease

Question 18

What are some common types of virulence factors? (5)

Answer 18

1. Adhesion factors
2. Nutrient acquisition (eg. iron sideophores)
3. Immune resistance (resistance to ROS)
4. Immune evasion/disruption (hide from immune system)
5. Extracellular enzymes, protein secretion systems/effectors and toxins (damage host)

Question 19

Describe adherence as a virulence factor

Answer 19

Microbes typically target specific cell or tissue type by adhering to specific receptors on those cells.
Provides foothold, facilitates interaction/invasion of host cells

Question 20

What are some examples of adherence factors? (adhesins)

Answer 20

Pili, fimbriae, surface proteins, capsules

Question 21

What are some common adherence receptors?

Answer 21

Glycoprotein, glycolipids

Question 22

How do pathogens evade the immune system

Answer 22

Hide inside cells
Produce capsule to hide surface antigens
Modify antigens e.g. pathogen associated molecular patterns (PAMPs) like LPS that are detected by immune system

Question 23

How do extracellular enzymes promote virulence

Answer 23

Free up nutrients, damage host cells, inactivate immune cell mechanisms, disrupt barriers to enable invasion

Question 24

Give two examples of extracellular enzymes.

Answer 24

S. aureus and coagulase, S. pyogenes and streptokinase

Question 25

What is the major secretion system is used by virulent pathogens?

Answer 25

Type III secretion system (T3SS), which is similar to T6SS

Question 26

How do T3SS work?

Answer 26

Inject effector proteins into host cells. Effectors have specific target to manipulate host cell biology, like inactivating signalling proteins.

Question 27

Aside from T3SS, what secretion system do other pathogens use?

Answer 27

Type IV secretion system, like L. pneumophila.

Question 28

What are exotoxins?

Answer 28

Secreted protein toxins, similar to bacteriocins, but target the host.

Question 29

Give an example of a bacterial toxin

Answer 29

Alpha-toxin from S. aureus. Proteins polymerize to form a pore.

Question 30

What are AB-type toxins

Answer 30

Subunit A exerts biological effect (modify/degrade specific molecules), Subunit B binds host cell glycoprotein/lipid to mediate uptake

Question 31

What are the two types of AB toxins?

Answer 31

AB and AB5

Question 32

Give an example of AB type toxin.

Answer 32

Botulinum toxin produced by clostridium botulinum.

Question 33

What does the A subunit do of botulinum toxin do? What does the B subunit do?

Answer 33

A subunit: protease that cleaves SNARE protens needed to release ACh
B subunit: targets motor neurons

Question 34

Botulinum toxin leads to what condition?

Answer 34

Muscle paralysis

Question 35

How are toxins used as therapeutics?

Answer 35

Inactivated toxins as vaccines
Treat non-bacterial diseases
Botox (botulinum toxin) = helps migraines, cerebral palsy

Question 36

How are toxins and secretion systems effector proteins different?

Answer 36

Toxins are more potent and diffuse/spread to distant cells.
SS effectors need direct contact with the cell and often work together.

Question 37

What causes the plague?

Answer 37

Yersinia pestis, a Gram negative proteobacterium.

Question 38

How does one aquire the plague?

Answer 38

Fleas, the disease vector, spread disease between rodents. Fleas bite people in the absence of rodents.

Question 39

What are the three types of plague?

Answer 39

Bubonic (lymph nodes), pneumonic (lungs), septicemic (bloodstream)

Question 40

What organism did Yersinia pestis evolve from?

Answer 40

Yersinia pseudotuberculosis, via several virulence adaptations that allowed it to hide from the immune system.

Question 41

What are some factors that allow Yersinia pestis to survive in fleas?

Answer 41

Yersinia murine roxin, a phospholipase D that appears to detoxikfy an unknown substance in flea guts.

Question 42

What is the main virulence of Yersinia pestis caused by?

Answer 42

T3SS injects effector proteins into immune cells
F1 capsule inhibits uptake of Y pestis by immune system, inhibits surface antigen detection