Corynebacterium diphtheriae. Corynebacterium genus and the diphtheroids

Question 1

General Features of Corynebacterium diphtheria

Answer 1

Gram +
Rod with “club-shaped” appearance in microscope

Metachromic (volutin) granules- storage of polyphosphate inside bacteria is a characteristic feature

Habitat- skin, mucosa of nose and throat (only human pathogen)

Question 2

Biochemical properties of Corynebacterium diphtheria

Answer 2

Catalase + and Saccharose -

Aerobic

Question 3

Pathogenesis of Corynebacterium diphtheria

Answer 3

Transmitted by respiratory droplets (aerosol)

Diphtheria Toxin- AB type toxin, composed of 2 Subunits: A = Active, B = Binding to receptor (only the toxin enters the blood, not the bacteria)

The toxins are adding ADP-ribose to eEF2
The ADP-ribose is inhibiting elongation (eEF2), thus inhibit protein synthesis

Inhibition of protein synthesis leads to cell death, which leads to the formation of pseudomembranes- made by a fluid that clot and enmesh leukocytes, fibrin, necrotic epithelial cell, cell debris and C. diphtheria, which adhere to the underlying tissue but can be pulled, causing bleeding

Question 4

Clinical Features (Diphtheria) of Corynebacterium diphtheria

Answer 4

Localized damage result from exotoxin production (bacteria always remains local):

Exudative pharyngitis with thick pseudomembranes that can spread to the larynx / trachea causing lymphadenopathy (“bull-neck” sign). If breaks off can cause airway obstruction (suffocation)

Systemic complications if the exotoxin spread to distant organs (toxemia):

Deep skin lesions (so called “skin diphtheria”)

Cardiac Effects: Myocarditis, arrhythmias, heart block and eventually heart failure

Neural Effects: (both motor and sensory nerves)
Demyelination- myelin fiber degeneration
Temporary paralysis of arms, legs or eye muscles, slurred speech, double vision

Question 5

Diagnosis of Corynebacterium diphtheria

Answer 5

Neisser staining- volutin granules become dark blue (A.K.A. polyphosphate, Babes-Ernst or energy granules), cytoplasm appears light which seen as “matchsticks” or “Chinese-letters” under microscope

Löffler medium- ivory-color appearance, made of clotted bovine serum, egg and heart extract. Rapidly growing with strong volutin granules formation (selective for C. diphtheria only)

Tellurite (Clauberg) medium- glycerin, blood, cysteine and tellurite (selective for the whole genus). Corynebacterium reduce tellurite forming grey to black colored colonies with garlic smell

Elek Test (to detect toxin)- Filter paper with antitoxin is submerged in medium with different strains. Lines of precipitation are seen where antitoxin and toxin of bacteria of interest are meeting

Römer Test- culture from Löffler medium is injected into Guinea pigs, one of which received anti-toxin

Question 6

Treatment of Corynebacterium diphtheria

Answer 6

Antitoxin (passive immunization) with Penicillin, Erythromycin or Aminoglycosides

Artificial ventilation (i.e. intubating) in case of airway obstruction

Question 7

Prevention of Corynebacterium diphtheria

Answer 7

DTP Vaccination (active immunization)- toxoid of diphtheria (i.e. attenuated toxin)

Question 8

C. ulcerans

Answer 8

Diphtheria-like disease (production of the same toxin), can cause tonsillitis.

Question 9

C. pyogenes

Answer 9

Ulcerating skin lesions.