Updated: 6/1/2018

Corynebacterium diphtheriae

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https://upload.medbullets.com/topic/104034/images/dirty_white_pseudomembrane_classically_seen_in_diphtheria_2013-07-06_11-07.jpg
Snapshot
  • A 4-year-old girl presents to the emergency room for a fever and sore throat. She recently visited Thailand for 2 months with her parents and had just flown back a couple of days ago. Her parents report that she has not had any of her recommended immunizations, as they have traveled all over the world. On physical exam, there is a grayish-white membrane covering her soft palate. When irritated by a tongue depressor, the membrane oozes with blood. She also has marked cervical lymphadenopathy and edema of the neck. She is immediately admitted for monitoring, antibiotics, and antitoxin.
Introduction
  • Classification
    • Corynebacterium diphtheriae
      • aerobic gram-positive rod
      • produces diphtheria toxin
    • transmission
      • respiratory droplets
  • Epidemiology
    • demographics
      • rare in the US
      • more common in developing countries
  • Pathogenesis
    • diphtheria exotoxin inactivates elongation factor (EF-2) via ADP-ribosylation
      • inhibits protein synthesis, causing necrosis in respiratory, cardiac and central nervous system tissue
      • affects mucous membranes, especially the respiratory tract
    • exotoxin is encoded by β-prophage
  • Associated conditions
    • diphtheria
    • cutaneous diphtheria
      • ulcerative lesions or cellulitis can occur independently of respiratory diphtheria
  • Prevention
    • DTap vaccine
      • vaccine against diphtheria, tetanus, and pertussis
      • 5 doses before school-age, completed by 4-6 years of age
    • Tdap vaccine
      • booster vaccine at 11-12 years of age
      • should also be given to pregnant mothers and those around them
    • Td vaccine
      • tetanus and diphtheria toxoid vaccine at 10-year intervals
  • Prognosis
    • symptoms are insidious
    • mortality is higher in young children, but generally good with prompt treatment
Presentation
  • Symptoms
    • fever
    • sore throat
    • malaise
    • may have a croup-like cough
  • Physical exam
    • pseudomembranous pharyngitis
      • gray or bluish white membrane seen on soft palate, tonsils, or back of the throat
      • bleeds easily if irritated
      • develops 2-3 days after symptoms
    • severe cervical lymphadenopathy
      • “bull neck”
    • myocarditis
    • arrhythmias
Studies
  • Bacterial culture
    • gram-positive rods with blue and red granules (metachromically) seen on culture
      • cysteine-tellurite agar (appears as black colonies)
      • Löffler medium
    • positive Elek test for diphtheria toxin
  • Making the diagnosis
    • most cases are clinically diagnosed and confirmed with a culture
Differential
  • Streptococcal pharyngitis
    • distinguishing factor
      • no pseudomembrane on mucous membranes
Treatment
  • Medical
    • diphtheria antitoxin
      • indication
        • all patients
    • antibiotics
      • indications
        • all patients
      • drugs
        • erythromycin
        • penicillin G
Complications
  • Airway compromise from soft tissue swelling
  • Heart failure from myocarditis
  • Secondary bacterial infection (e.g., pneumonia)

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Questions (5)
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(M1.MC.14.71) A 6-year-old male who recently immigrated to the United States from Asia is admitted to the hospital with dyspnea. Physical exam reveals a gray pseudomembrane in the patient's oropharynx along with lymphadenopathy. The patient develops myocarditis and expires on hospital day 5. Which of the following would have prevented this patient's presentation and decline?

QID: 101530
1

Increased CD4+ T cell count

5%

(4/82)

2

Secretory IgA against viral proteins

7%

(6/82)

3

Increased IgM preventing bacterial invasion

10%

(8/82)

4

Circulating IgG against AB exotoxin

77%

(63/82)

5

Improved IgE release from mast cells

1%

(1/82)

M 1 E

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(M1.MC.14.1) A 12-year-old male whose family recently emigrated from eastern Europe presents to the emergency room with a fever of 103.5F, a swollen neck (Figure A), difficulty breathing, and grayish-white membranes in the oropharynx (Figure B). Cultures were taken from the pharynx and the bacteria were found to be Gram-positive rods with metachromatic granules (Figure C). The toxin produced by this bacterium has which of the following mechanism of action?

QID: 106293
FIGURES:
1

Pertussis toxin inhibits the G-protein Gi alpha subunit via ADP ribosylation

13%

(9/68)

2

Overactivates guanylate cyclase

1%

(1/68)

3

Inactivates the 60S ribosomal subunit

10%

(7/68)

4

Inactivates elongation factor 2

68%

(46/68)

5

Cleaves SNARE proteins

4%

(3/68)

M 1 E

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(M1.MC.13.175) A 3-year-old male is brought to the ER with a sore throat and fever. Examination of the pharynx reveals a dark, inflammatory exudate. Cysteine-tellurite agar culture produces black, iridescent colonies. Microscopic features of the causal organism most likely include which of the following?

QID: 101634
1

Serpentine growth patterns

11%

(23/215)

2

Metachromic granules

32%

(68/215)

3

Lancet-shape

17%

(36/215)

4

Long, branching filaments

16%

(35/215)

5

Kidney-bean shaped rod

13%

(28/215)

M 2 E

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