Lec #1 (Wk 2): Diphtheria

Question 1

What organs make up the upper respiratory tract? Lower respiratory tract? Is diphtheria upper or lower respiratory tract infection?

Answer 1

Upper: Nasal cavity, pharynx, & larynx.
Lower: trachea, bronchi, & lungs.

Diphtheria is an upper respiratory tract infection.

Question 2

How many sub-species does diphtheria have? List them.

Answer 2

4
C. Diphtheria Mitis
C. Diphtheria Intermedius
C. Diphtheria Gravis
C. Diphtheria Belfanti

Question 3

What bacteria is responsible for Diphtheria?

Answer 3

Corynebacterium Diphtheriae

Question 4

What is diphtheria & who does it usually affect?

Answer 4

It is a CONTAGIOUS infectious disease affecting the upper respiratory tract (Respiratory diphtheria) and appears in children aged 1-5.

Question 5

What are the symptoms of diphtheria?

Answer 5

1- Sore throat (difficulty in swallowing).
2- Swollen neck gland (Bull neck appearance).
3- Adherent membrane on the tonsils called PSEUDOMEMBRANE.
4- Localized skin infections.

**Some are asymptomatic carriers which is dangerous.

Question 6

How does C. Diphtheriae cause diphtheria?

Answer 6

C. Diphtheriae usually happens in those who didn’t get the vaccine or are immunocompromised. It is transmitted by respiratory droplets like sneezing or coughing. Then the C. diphtheria attaches to the epithelial cells of the pharynx (Infection starts at the nasopharynx), then once there it releases DT toxins which causes a local inflammation that leads to necrosis & neck swelling. Necrotic tissues build up in the pharynx which causes the grey adherent leathery membrane known as PSEUDOMEMBRANE.
This pseudomembrane covers the posterior pharynx & may extend way behind to cause obstruction & hence suffocation. If left untreated, it can gradually invade deeper into the pharyngeal wall till it reaches the bloodstream thus moves to the heart & causes myocarditis.

Question 7

Where does diphtheria infection start?

Answer 7

Nasopharynx.

Question 8

What does corynebacterium diphtheriae stand for?

Answer 8

Coryne –> club-shaped.
Diphtheriae –> leather like membrane (Referring to the pseudomembrane).

Question 9

Talk about the corynebacterium diphtheria; as in its gram stain, shape, & oxygen demand.

Answer 9

• Gram positive
• Club-shaped bacilli.
• Has metachromatic granules (circles on the head of bacilli)
• Non-motile (no flagella)
• Non-encapsulated
• Aerobic
• Non-spore forming
• Arranged in V-shapes where it looks like Chinese letters/Cuneiform arrangement or some have a palisade arrangement where they are parallel to each other.

Question 10

What does metachromatic granules(AKA Volutin) mean?

Answer 10

Large inclusions found on the head of bacilli which is filled with inorganic phosphates to be used in ATP synthesis.
(Search up on google ‘Metachromatic Granules Diphtheria’, the red circles on top are the metachromatic granules)

Question 11

What is the arrangement of the C. Diphtheriae cells?

Answer 11

1- Chinese letters / Cuneiform arrangement that is V-shaped.
2- Palisades (stacked parallel on top of one another).

Question 12

How are C. diphtheria classified?

Answer 12

According to their morphological appearance in the culture. The culture is a Tellurite containing media.
Mitis –> Black colonies with gray peripheries.
Gravis –> Large grey (in the pic they are acc white) colonies.
Intermedius –> tiny black circles.
(search up on google Mitis colonies diphtheria, look at 1st pic with all 3 comparison).

Question 13

What important culture media is used for Corynebacterium diphtheriae?

Answer 13

Tellurite containing media

Question 14

A patient is presented with bull neck, this is a characteristic of?

Answer 14

Diphtheria.

Question 15

When culturing the C. diphtheria, what are we expected to see?

Answer 15

Colonies.

Mitis = black colonies with gray at the periphery.

Gravis = large gray colonies.

Intermedius = tiny black colonies

Question 16

How does C. Diphtheriae cause infection?

Answer 16

Releases virulence factors.

Question 17

C. Diphtheria is normally avirulent, so what made it virulent? Say the story.

Answer 17

This bacteria was peacefully sitting, until it was infected by a virus (bacteriophage) and this bacteriophage kept on multiplying. The chromosome of this bacteriophage can get incorporated into the bacterial plasmid (Although this is rare, happens 1 in 10,000) and once incorporated the plasmid is now called a prophage. The chromosome of the bacteriophage contains Tox gene. The entire bacteria is called a lysogenic bacteria. This lysogenic bacteria can divide at the same rate as any normal bacteria.
TOX GENE is the virulent factor.

Question 18

What is the virulence factor of diphtheria?

Answer 18

Bacteriophage tox gene. This bacteriophage chromosome can get incorporated into the bacterial plasmid.
**C. DIPHTHERIAE THAT DON’T CARRY THIS TOX GENE IS NOT VIRULENT. THE TOX-GENE IS THE VIRULENT FACTOR.