Diptheria: Corynebacterium diphtheriae

Question 1

Classify C. diphtheriae

Answer 1

Gram +
Non-spore forming
Bacillus (rod shaped)
Aerobic
Non-motile

Question 2

What does this microbe look like under a microscope?

Answer 2

Chinese letters (irregular, club shaped)

“Koryne” = club

Question 3

What is required for this microbe to be virulent?

Answer 3

Diphtheria toxin (Dt), coded by the tox gene

Question 4

How does this microbe become virulent?

Answer 4

Lysogenic conversion

–lysogenic beta-prophage “infect” and transfer the tox gene into C. diphtheriae

no phage, no virulence

Question 5

Characterize diphtheria toxin (Dt):

Answer 5

“The AB Model”

A = toxic subunit: ADP ribosylated elongation factor 2 (EF2), thereby disrupting protein synthesis in the cell.

B = adhesin subunit: binds to heparin-bindng EGF on cell surfaces, allowing the toxin to be endocytosed

Question 6

How potent is Dt?

Answer 6

Extremely potent… One molecule is enough to kill one cell.

Question 7

How does diphtheria infection present?

Answer 7

1) Very sore throat + psuedomembrane on tonsils, oral cavity, and pharynx.
2) Prominent neck swelling (severe disease)
3) Nonspecific skin lesions (cutaneous diphtheria)

Question 8

If the initial infection goes untreated, how does it ensue?

Answer 8

Necrotic tissue in oral cavity/skin will release Dt into the blood, causing organ damage, especially in the HEART and CRANIAL NERVES/BRAIN

Question 9

What do you do if you suspect diphtheria infection?

Answer 9

1) Carefully swab the psuedomembrane (so as to not cause rupture) and send it off to a special lab. (REQUIRED for dx)
2) Notify the CDC
3) Order additional tests (neck CT, EKG)
4) Treat the patient immediately and also anyone in close contact (prophylactically)

Question 10

What is the treatment for diphtheria?

Answer 10

1) Antitoxin: neutralizes circulating Dt (not Dt already bound); do this for symptomatic, diffuse cases
2) Antibiotics: erythromycin/penicillin