Module 12: Bacterial Pathogenesis (Cytotoxins + Superantigens)

Question 1

Cytolysins

Answer 1

Cytotoxins that act on plasma membranes

Question 2

What propotion of bacterial protein toxins do cytolysins make up?

Answer 2

Cytolysins = >1/3 of all bacterial protein toxins

Question 3

What are cytolysins named based upon?

Answer 3

1) Origin, 2) Order of discovery, 3) Cells they destroy

Question 4

Hemolysin

Answer 4

Cytolysins that lyse RBCs

Question 5

Hemolysis

Answer 5

Destruction of RBCs

Question 6

What is a method we can use to identify streptococcus species?

Answer 6

Hemolysis patterns when plated on blood agar!

Question 7

What are the distinct hemolysis patterns produces by streptococcus species?

Answer 7

Alpha-hemolysis (S. pneumoniae) = Partial Hemolysis

Beta-hemolysis (S. pyogenes) = Complete hemolysis

Gamma-hemolysis (enterococcus faecalis) = NO hemolysis

Question 8

What is the hemolysis pattern of S. pyogenes?

Answer 8

Beta-hemolysis == COMPLETE hemolysis

(Fully clear zone)

Question 9

What is the hemolysis pattern of S. pneumoniae?

Answer 9

Alpha-hemolysis = PARTIAL hemolysis

(green-tinged zone)

Question 10

What is the appearance of alpha, beta, and gamma hemolysis?

Answer 10

Alpha = Green-tinged zone

Beta = Completely cleared zone

Gamma = No clearing or anything

Question 11

What causes the green coloration of alpha-hemolysis?

Answer 11

Partial hemoglobin degradation

Question 12

What are the general categories of cytolysins?

Answer 12

1) Pore-forming toxins

2) Membrane-damaging toxins (AKA Lecithinases or MDTs)

Question 13

What are pore-forming cytolysins?

Answer 13

Cytolysins that are produced as MONOMERS which polymerize/oligomerize within membranes to form a circular pore!

Question 14

What do pore-forming cytolysins bind to?

Answer 14

Bind to receptors on host cells that are specifically only found concentrated in eukaryal cells and NOT concentrated within bacterial cells!

(Prevents the toxin from binding to the bacterium and damaging itself!)

Question 15

What is an example of a well-characterized pore-forming toxin?

Answer 15

ALPHA-TOXIN

(found in S. aureus)

Question 16

S. aureus alpha-toxin process:

Answer 16

1) S.aureus produces and then secretes alpha-toxin MONOMERS into the ECF

2) Alpha-monomer binds to a receptor on the host cell surface

3) Other alpha-monomers oligomerize on the bound monomer

4) Oligomerization results in a conformational change

== hydrophobic domains of the monomers insert into the PM forming a PORE complex

5) Pore allows for inflow from ECF, disrupting water/ion balance == could lead to lysis or apoptosis (depending on size and # of pores)

Question 17

The type and extent of damage induced by cytolysins depends on…

Answer 17

Their CONCENTRATION within the body

Question 18

High concentration of cytolysins leads to…

Answer 18

DIRECT LYSIS (necrosis)

–> Many large holes are formed in the cell membranes, causing so much damage that the cell just bursts open

== (dangerous for other nearby cells!)

Question 19

Low concentrations of cytolysins leads to…

Answer 19

Ca²⁺ Influx —> APOPTOSIS

–> Few small pores form within the membrane; cause damage to the membrane WITHOUT lysing the cell!

–> Ion fluxes are promoted = Ca²⁺ is admitted into the cell which causes apoptosis if prolonged uptake occurs

Question 20

Other than hemolysin, what is another example of a cytolysin?

(origin, target, effect)

Answer 20

Perfingolysin (causative agent of gas gangrene)

–> origin = Clostridium perfinges
–> target = binds to CHOLESTEROL within eukaryal PMs
–> effect = causes necrosis of the muscle + excessive gas production within tissues

Question 21

What bacterial element cases gas gangrene?

Answer 21

The cytolysin PERFINGOLYSIN produced by Clostridium perfinges

Question 22

What produces the gas in gas gangrene?

Answer 22

C. perfinges metabolizing carbohydrates anaerobically

Question 23

Superantigens

Answer 23

Exotoxins with the ability to activate CD4+ cells

Question 24

What are CD4+ cells AKA?

Answer 24

HELPER T-cells!

Question 25

Overall (not in depth), how do superantigens activate helper T-cells?

Answer 25

By directly CROSSLINKING the TCR of Helper T-cells to the MHCII of antigen presenting cells (even with no antigen present)

Question 26

What do CD4+ T-cells typically do?

Answer 26

Typically release cytokines upon activation by antigen binding --> Cytokines that get released are meant to trigger other immune cells to activate and attack the component containing the detected antigen

Question 27

Normal Helper T-Cell Activation Process

Answer 27

1) Antigen Presenting Cell (APC) presents an antigen bound to its MHCII 2) A helper T-cell with the complementary TCR "recognizes" this antigen by binding to it via its TCR 3) CD4 coreceptor complementarily binds to the MHCII of the APC as a secondary interaction 4) Binding of BOTH the CD4 coreceptor and TCR == Helper T-cell gets activated! 5) Activation triggers expansion of that specific T-cell population (with the same TCRs) 6) The expanded population of T-cells release cytokines into the area of activation to recruit other fighting immune cells

Question 28

The response initiated by NORMAL Helper t-cell activation is...

Answer 28

Controlled, localized, and ANTIGEN DEPENDENT

Question 29

Superantigen T-cell Activation Process:

Answer 29

1) Antigen presenting cell is unbound/not bound to the matching antigen with a given T-cell == no interaction between APC and T-cell 2) Superantigen comes along and binds to the MHCII of the APC and the TCR of the T-cell, forcing the two to come together (crosslinking) 3) T-cell is "wrongfully" activated! == Begins clonal expansion (even though that t-cell is not needed) 4) Process repeats with all kinds of T-cells with distinct TCRs resulting in a massive heterogenous, unspecific T-cell population 5) The population all release cytokines == extensive amount of cytokines present 6) Large amount of cytokines triggers massive inflammatory response (usually systemic) which can be damaging

Question 30

Normally, how many T-cells are activated by a given antigen?

Answer 30

< 0.001% of body's total # t-cells --> Activation is highly specific!

Question 31

With superantigens present in the blood, how many T-cells can be activated

Answer 31

Up to 20% of body's total # t-cells --> Activation is highly random, unspecific, and uncontrolled

Question 32

Superantigens are particularly dangerous when...

Answer 32

they get into the bloodstream! (can cause systemic response leading to shock + death)

Question 33

Upon superantigens entering the bloodstream, what are two main cytokines released by activated t-cells?

Answer 33

IL-2 and IL-1

Question 34

IL-2 vs IL-1

Answer 34

**IL-2** = T-cell growth factor that promotes t-cell expansion **IL-1** = Potent proinflammatory cytokine

Question 35

What are some examples of potent pro-inflammatory cytokines?

Answer 35

IL2, TNF-alpha, IFN-gamma

Question 36

Toxic Shock Syndrome

Answer 36

(TSS) A superantigen induced systemic shock that can lead to multi-organ failure and death

Question 37

Do all superantigens lead to TSS? Why or why not?

Answer 37

No not all lead to TSS --> Because all exhibit different potency (strength) + level of expression (how much is present within body)

Question 38

What is an example of a superantigen that does not lead to TSS?

Answer 38

S.aureus Enterotoxin

Question 39

Enterotoxin

Answer 39

Secreted toxins that primarily act upon the gut --> Superantigens characterized by weak superantigen ability!

Question 40

How do the enterotoxins produces by S.aureus get INTO us?

Answer 40

Via our food (especially food that has not been properly stored or cooked)

Question 41

How does S.aureus end up in our food in the first place?

Answer 41

S. aureus colonizes our skin and nasal cavity == if we touch/prepare food, we likely get the bacteria on that food --> To prevent its growth and enterotoxin production we cook food (to kill S.aureus) and store it properly (to prevent growth)

Question 42

How can we mitigate the production of enterotoxins that get into our food?

Answer 42

We CANT destroy the enterotoxin itself (very heat resistant) BUT we CAN try to kill the S.aureus that produces it to prevent its formation in the first place == Cooking to temperature > 60C AND storing at temperatures <7.2C

Question 43

How many individuals are colonized by S.aureus?

Answer 43

20-50% of individuals (and 20-50% of those colonies are enterotoxigenic)