(VII) Gram Positive Rods Aerobic (2)*Corynebacterium diphtheriae

Question 1

Characterize (2) : Corynebacterium diphtheriae

Answer 1

(1) Gram (+) club shaped
(2) Metachromatic granules

Question 2

Corynebacterium diphtheriae

Transmission: […]

Virulence:
Diphtheria toxins (some strains) - blocks protein synthesis

Clinical presentation:
[…]

Answer 2

Corynebacterium diphtheriae

Transmission: respiratory dropets, spread aided by asymptomatic carriers

Virulence:
Diphtheria toxins (some strains) - blocks protein synthesis

Clinical presentation:
Diphtheria 白喉

1. Local effects of toxin:
   - Pharyngeal infection (nasal, laryngeal, tracheal sites), sore throat, malaise, fever
   - Pseudomembrane formation (dirty white, becoming darker with time, may obstruct airway)
   - infected area becomes red & swollen (may result in airway obstruction and “bull neck” – tissues of neck become very swollen)
   - Palatal paralysis
2. Distant effects of toxin:
   - myocarditis (+/- arrhythmias and heart failure, potentially fatal)
   - Neuropathy (Visual disturbance, limb paralysis, difficulty swallowing)

Pseudomembrane formation in c.diphtheriae is pharyngeal while in c.diff its in the gut (colitis)

Question 3

Corynebacterium ulcerans leads to throat infections and sometimes […]

Answer 3

Corynebacterium ulcerans leads to throat infections and sometimes full blown diphtheria

Question 4

Diagnosis for diphtheria must be […]

Bacteriological:
[…]

Answer 4

Diagnosis for diphtheria must be CLINICAL

Bacteriological:
Throat swab PCR or culture. Need special selective medium so warn the lab!!

Go for early treatment, dont wait for tests.

Identify colonies (culture), check for toxin production (PCR)

Question 5

Diphtheria is a toxin mediated disease carried by a […].
- B fragment […], A fragment […]
- Toxin particularly damages […] & […]

Answer 5

Diphtheria is a toxin mediated disease carried by a phage.
- B fragment binds, A fragment inactivates EF2 (and hence protein synthesis)
- Toxin particularly damages nerves & heart muscles

Question 6

Histology of C. diphtheriae shows […]

Answer 6

Histology of C. diphtheriae shows chinese characters

Tho I have no idea how this unorganized and unsophisticated mess resembles chinese characters

Question 7

The special selective medium for C. diphtheriae is […]

Answer 7

The special selective medium for C. diphtheriae is Tinsdale’s medium

Grows as brown colonies with brown halo

The other medium is Elek plate (precipitin line indicates toxigenic strain)

Question 8

What is the treatment for diphtheria?

[…]

Answer 8

What is the treatment for diphtheria?

Antiserum (neutralize toxin), erythromycin/penicillin, isolation (infection control), supportive/symptomatic treatment

vaccination (toxoid) and prophylatic antibiotics (pt and contacts) for prevention