Lecture 12 Gram + rods, exotonis and Koch's postulate

Question 0

What are Koch’s postulates?

Answer 0

1) Microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy animals.
2) The microorganism must be isolated from a diseased organism and grown in pure culture.
3) The cultured microorganism should cause disease when introduced into a healthy organism.
4) The microorganism must be re isolated from the inoculated, diseased experimental host and ID’ed as being identical to the original specific causative agent.

Question 1

Robert Koch studying Gram + spore- forming bacillus developed a set of criteria, to determine the causal agent of disease. What was it called?

Answer 1

By Koch’s postulates

Question 2

What are the characteristics of Corynbacterium diptheriae?

Answer 2

• Large group of gram positive +
• Non spore forming
• Non motile
• Rods (bacilli)
• Colonize the skin, upper respiratory tract, and GI tract
• Can fxn as opportunistic pathogen

Question 3

What does C. diphtheriae cause?

Answer 3

Diphtheria, multiply locally on epithelial cells in the pharynx.

Question 4

What is the pathology of diphtheria?

Answer 4

Directly related to the exotoxin secreted by C. diphtheriae at the site of infection.

• A-B exotoxin production occurs only when the bacillus is itself stably infected (lysogenized) by a specific virus (bacteriophage) carrying the genetic information for the toxin.
• Organism does not need to enter blood stream to produce systemic signs.

Question 5

How does an A-B toxin work?

Answer 5

The B subunit binds primarily to heart and nerve cells. After the toxin attaches to the cell the A subunit enters the cytoplasm.

• The A subunit then terminates host protein synthesis by inactivating (ribosylates) elongation factor -2 (EF-2), a factor required for the movement of nascent peptide chains on ribosomes.
• Since it works as an enzyme one single molecule of diphtheria toxin is enough to inhibit all protein synthesis is a cell.

Question 6

How is C. diptheriae maintained in the population?

Answer 6

It is maintained by asymptomatic carriage in the throat of immune individuals.
* Transmitted by respiratory droplets.

Question 7

What is distinctive (unique) *about the infection produced by C. Diphtheriae?

Answer 7

It forms a thick, gray-white, adherent exudate- called a “pseudomembrane” because it is not real. It is difficult to dislodge w/out making the underlying tissue bleed.

Question 8

What is the pseudomembrane composed of?

Answer 8

bacteria, cellular debris, and inflammatory cells that can cover the tonsils, uvula, and plate and extend deep into the throat.
***This may eventually cause suffocation

Question 9

What happens when C. diphtheriae disease progresses?

Answer 9

Generalized systemic symptoms appear due to the A-B exotoxin.

• cardiac and nerve pathology
• untreated 40% mortality, Tx = 10%

Question 10

What is the most important aspect of treatment for C. Dip

Answer 10

Antiserum therapy to treat!
*Early administration of anti-toxin to specifically neutralize the exotoxin.

***Prevented by immunizing (as vaccines) with diphtheria toxoid (doesn’t cause pathology, but is **still immunogenic)

Question 11

Where was there a massive reemergence of Diphtheria ?

Answer 11

In the Newly Independent States of the former Soviet Union marked the first large-scale diphtheria epidemic in industrialized countries since the 1950s. 
-Factors:
susceptible adults
decreased childhood vaccines
low socioeconomic conditions

Question 12

Which organisms are spores (endospore)?

Answer 12

“Some” gram-positive, but NEVER gram-negative bacteria.

Example: Clostridium and Bacillus (BOTH* soil bacteria)

Question 13

How doe these bacteria become spores?

Answer 13

Under certain harsh conditions they change from vegetative state to dormant state, “a spore”.

Question 14

What is a spore?

Answer 14

a dehydrated, multi shelled structure that protects and allow the bacteria to exist in suspended animation for a incredible period of time.
**They are difficult to decontaminate with standard disinfectant procedures.

Question 15

What is it made up of?

Answer 15

Complete copy of the chromosome and a bare minimum of proteins and ribosomes.
-Has an inner membrane a peptidoglycan cortex and a thick outer keratin-like protein coat.

Question 16

What does the structure of the spore protect?

Answer 16

It protects the DNA from desiccation, heat, radiation, and attack by most enzymes and chemicals.

Question 17

Which spores are highly resistant and why?

Answer 17

bacterial spores are thick walled structures formed by vegetative cells during sporulation.
**Most resilient forms of life b/c they can resist radiation, chemicals,high temperatures, desiccation and harmful environments.

Question 18

What are characteristics of Clostridium?

Answer 18

• All obligate anaerobic
• gram positive bacilli
• capable of forming spores
• ubiquitous

Question 19

What are some human pathogens of Clostridium?

Answer 19

1) C. tetani –> Tetanus
2) C. botulinum–> Botulism
3) C. perfringes–> Gas gangrene, food poisoning
4) C. difficile–>Antibiotics colitis

Question 20

Which Clostridium species secrete A-B exotoxins ?

Answer 20

1) C. tetani 2) C. botulinum (MOST potent toxins known)

Question 21

What does C. tetani cause?

Answer 21

Causes Tetanus which is rare in the US b/c of vaccination.

Question 22

What population is mostly affected?

Answer 22

Newborns (20-50% mortality)

Question 23

Where do C. tetani spores germinate?

Answer 23

• in a deep wound where anaerobic conditions are found.

- They multiply locally and secrete AB exotoxin

Question 24

How does the A-B work? and what does it target?

Answer 24

Targets neurons and the A subunit blocks the neurotransmitter release at inhibitory synapses.
RESULT: **severe prolonged muscle spasms= spastic paralysis

Question 25

What is C. botulinum?

Answer 25

Typically causes disease when spores or toxin are consumed in food.

Question 26

How is the paralysis different between Tetanus and Botulism?

Answer 26

Tetanus = spastic paralysis (continual stimulation of muscle) ex:lock jaw.
*Blocks inhib-neuron release

Botulism= Flaccid paralysis (No muscle stimulation)
*Blocks release of acetylcholine

Question 27

What is the most common form of Botulism?

Answer 27

Infant botulism, which is associated with honey, home-canned, low-acid foods, contaminated with spores.

Question 28

In infants where do the spores germinate?

Answer 28

In the gut and the bacteria multiply locally, and secrete A-B toxin into blood.

Question 29

How does the botulinum and tetani toxin target cells compare ?

Answer 29

Similar to tetani the botulinum targets the cholinergic nerves

Question 30

How does the A-B toxin affect the muscle?

Answer 30

it blocks the releae of the neurotransmitter acetylcholine, this prevents muscle contraction causing flaccid paralysis.
**Death occurs from paralysis of respiratory muscles

Question 31

Is Botulism considered a true food poisoning?

Answer 31

• Yes, because Botulism can occur from consuming toxin-contaminated foods.
• Ingestion of the toxin present in the improperly prepared food causes the disease.

Question 32

What bacteria is commonly seen in an dirty wound?

Answer 32

C. tetani they produce from that local infection an A-B exotoxin that goes systemic.

Question 33

Why are boosters required to maintain immunity?

Answer 33

The protective immunity begins to wane slowly after vaccination, and usually doesn’t last a lifetime.
(Should be done every 5-10 yrs)

Question 34

What is C. perfringes?

Answer 34

It causes Gas gangrene and food poisoning.

Question 35

How is gas gangrene caused?

Answer 35

Spores C. perfringens infect any dirty deep (anaerobic) wound or cut

Question 36

What kind of exotoxins do C. perfringes cause?

Answer 36

Huge number of mostly Cytolytic exotoxins and spreading factors.

Question 37

What does C. perfringens cause food poisoning?

Answer 37

Results from eating meat left out too long after cooking these spores have germinated before eating.
**Once in the small intestine the C. perfringens release a toxin that often causes abdominal cramping and diarrhea

Question 38

What is antibiotic associated colitis?

Answer 38

(C. difficile, Pseudomembrabonous colitis)

**The antibiotics alter the normal GI flora, allowing the overgrowth of exotoxin producing C. difficile

Question 39

What is bacillus anthracis?

Answer 39

• Gram positive spore former, found in soil.
• Has a capsule !!!
• ** It primarily infects grazing mammals that ingest the spores.

Question 40

What are the 3 types of Anthrax in humans ?

Answer 40

1) Cutaneous: anthrax acquired when a spore enters the skin thru a cut.
2) Pulmonary (inhalation) anthrax from breathing in airborne anthrax spores.
3) Gastrointestinal tract anthrax, contracted from eating contaminated food, primarily meat from an animal that dies of the disease.
(Bacillus cereus?)

Question 41

What toxins cause Anthrax?

Answer 41

2 potent A-B exotoxins

Edema Toxin and Lethal Toxin – that together cause edema and shock

Question 42

Why is B. anthracis an excellent bioterrorism weapon?

Answer 42

It is commonly found and easy to grow and produces hardy spore that could be dispersed into a community causing huge infections/deaths.
***Systemic AB exotoxin

Question 43

How does B. Anthracis infects humans?

Answer 43

• Humans are affected by handing infected animals or their products. Spores germinate locally (facultative). Macrophages act as “taxis” and take the bacteria deeper in to the body.
• Macrophages are eventually killed by the bacteria.
• They will release in the blood “causing bacteremia” (via capsule) and proliferate and cause disease by releasing AB exotoxins (major virulence factor) that cause massive edema and shock.