Bacterial Toxins & Metabolism

Question 1

Explain the differences between endotoxins and exotoxins regarding their production, chemical nature, immunogenicity, and toxicology

Answer 1

Endotoxins:
-LPS of cell wall (main) (only gram negative); peptidoglycan and lipo/techoic acids (gram positive) (fever and drop in blood pressure)
-heat-stable, vigorous immune response, responsible for septic shock, fever, and disseminated intravascular coagulation (DIC)
-not a good toxoid
Exotoxins:
-very specific damaging effects, most potent toxins known & major cause of damage to host
-secreted by bacterium or leak into surrounding tissue following cell lysis
-toxins act locally or systemically
-made of protein – heat labile and good toxoids
-fatal damage can occur before adequate immune response is mounted
-antitoxin can be given as treatment
-3 functional categories: cytotoxins, enterotoxins, neurotoxins
-classes: AB toxins, membrane damaging toxins, and superantigens

Question 2

Define cytotoxins

Answer 2

• damage to a variety of cells

- damage caused by interference w/ cell function or cell lysis

Question 3

Define enterotoxins

Answer 3

• damage to digestive tract

- major symptoms are vomiting and diarrhea

Question 4

Define neurotoxins

Answer 4

• damage to nervous system

- major symptom is paralysis

Question 5

Describe AB toxins

Answer 5

• A unit = active/toxic subunit
• B unit= binding subunit
• can use B subunit for vaccines

Question 6

Describe membrane damaging toxins

Answer 6

• disrupts plasma membrane/causes cell lysis
• some toxins produce pores in membrane to allow fluids in causing cell destruction
• phospholipases are part of this group
  
  • remove polar head groups of phospholipids (destabilizes membrane)

Question 7

Describe superantigens

Answer 7

• override specificity of T-cell response/overactivates
• massive release of cytokines by large number of helper T cells
• binds MHC Class II and T cell receptor

Question 8

Differentiate between aerobic respiration, anaerobic respiration and fermentation

Answer 8

Aerobic respiration: oxidizing agent is O2
Anaerobic respiration: oxidizer is non-O2 inorganic molecule such as nitrate or sulfate
Fermentation: oxidizer is organic (derived from food)
Efficiency: aerobic > anaerobic; repiration > fermentation

Question 9

Define toxoid

Answer 9

chemical/heat treated exotoxin that has lost toxicity but retains antigenicity

• used as a vaccine
• cannot use for endotoxins

Question 10

Define antitoxoid

Answer 10

antibodies produced in an animal immunized with toxoid or toxin
-neutralize toxin for treatment and emergency immunization

Question 11

Illustrate aerobic respiration in the context of glucose oxidation

Answer 11

pyruvate is completely oxidized by O2

- 38 ATP, CO2, H2O

Question 12

Illustrate anaerobic respiration in the context of glucose oxidation

Answer 12

pyruvate is completely oxidized by nitrate or sulfate

-34 ATP + NH3 + H2S

Question 13

Illustrate fermentation in the context of glucose oxidation

Answer 13

organic oxidizer is pyruvate or derivative

after recieving electrons, pyruvate is converted to small organic acids or alcohols + 2 ATP

Question 14

Differentiate between aerobic, facultative and anaerobic bacteria

Answer 14

Aerobic: requires O2
Facultative: prefers O2, but anaerobic or fermentation possible
Anaerobic: inhibited or killed by O2

Question 15

Which anaerobe is most adaptive?

Answer 15

Facultative

Question 16

What are aerotolerant anaerobes?

Answer 16

doesn’t use O2 but tolerates it

Question 17

Explain why oxygen is toxic to cells and how aerobes detoxify reactive oxygen species

Answer 17

• O2 is a strong oxidizer and will kill anaerobes

- O2 ETC leaks electrons –> forming reactive oxygen species that destroy lipids and DNA easily