Corynebacterium diphtheriae is a gram-positive, club-shaped bacterium that causes diphtheria. It produces a powerful exotoxin that inhibits protein synthesis and causes the formation of pseudomembranes at infection sites. Diagnosis involves isolating the bacterium from throat swabs and performing biochemical and virulence tests. Treatment consists of antitoxin and antibiotics like penicillin or erythromycin. Active immunization with diphtheria, pertussis, and tetanus vaccine helps prevent diphtheria.

1. Corynebacterium
Dr. Kanwal Deep Singh Lyall
M.D. Microbiology

2. • Gram positive, non-sporing, non-AFB, non-
motile
• Corynae = club shaped
• Aerobes, catalase positive, oxidase – ve

3. C. diphtheriae
• Bretonneau (1826) – named diptherite
(diptheros = leather) – pseudomembrane
• Klebs – Loeffler bacillus
• Roux & Yersin – discovered exotoxin
• Von – Behring (1890) – antitoxin – Nobel prize

4. • Club shaped
• Metachromatic granules (bluish purple with
Methylene blue) – Volutin/ Babes – Ernest
Granules
• Polymetaphosphate granules – energy depots
• Arrgangement – chinese letter / cuneiform
• Stains – Alberts (Bacilli – green, Granules –
bluish black) , Neisser’s

6. Culture
• Require blood, serum , egg
• LSS – Loeffler’s serum slope – 6 – 8 hrs
• Blood tellurite medium – 48 hrs – Gravis,
Mitis, Intermedius
• Tinsdale’s medium
• Sugars – Hiss serum sugars – Glucose, Maltose
– acid only

8. Toxin
• Powerful exotoxin
• Heat labile
• Park – Willam 8 strain
• Tox gene – Beta phage – lysogenic conversion
• Protein (62000 kd) = Fragment A (24000,
enzymatic) + Fragment B (38000, Binding)
• Inhibits polypeptide chain elongation –
protein synthesis (In presence of NAD) –
Inactivates EF2
• Toxoid – 37 C x 4 – 6 hrs, formalin, acidic pH

10. Pathogenesis
• m/c age affected 2 – 10 years, unvaccinated
• Droplets – IP 3-4 days
• Faucial (m/c) , Laryngeal , nasal, conjunctival ,
otic, vulvo-vaginal, cutaneous
• No bacteremia
• Local – entry site – Pseudomembrane
(Epithelial cells, WBCs, RBCs, fibrinous
exudate & bacteria) – mechanical effects
• Systemic – Toxin has affinity for cardiac,
adrenals, kidney, liver

11. Complications
• Local – obstruction , asphyxia – death
• Systemic – myocarditis, polyneuritis, post –
diptheric paralysis
• Degeneration
of tissues

12. Lab diagnosis
• Only for control measures and epidemiological
purposes
• Treatment should not await lab results
• Requires – isolation of organism and virulence
tests

13. Sample : swabs
Staining : Gram’s ( Vincent’s angina =
Spirochaets + fusiform bacilli)
& Albert’s stain
Culture
LSS BTA BA
6 – 8 hrs 48 hrs Staph /
Strept
Small, circular, creamy Black
Staining & Biochemical tests
Virulence tests
In Vitro tests In Vivo
Eleck’s gel precipitation test
Tissue Culture
Subcutaneous &
Intradermal tests

17. Prophylaxis
• Active immunization : DPT
• Passive immunization : ADS (Horse)
• Combined : ADS + DPT
• Schick test:
• intradermal test to demonstrate circulating
antitoxin
• 0.2 ml (1/50 MLD), 1st, 4th , 7th days and toxoid
• Positive = susceptible, negative = immune,
pseudo-reaction = immune + hypersensitive,
combined reaction = susceptible + hypersensitive

19. Treatment
• ADS (20,000 – 100,000) + Antibiotics
• Penicliin , erythromycin
• Erythromycin for carriers

20. Other corynebacteria
• C. ulcerans – throat ulcers
• C. pseudotuberculosis – Preiz – Nocard bacillus,
C. ovis – human infection – milk
• C. jekium – infection in neutropenics, multidrug
resistant, treatment – Vancomycin
• Diptheroids: commensals – throat, skin,
conjunctiva – mistaken for C. diptheriae
• C. pseudodiptheriticum – throat
• Arranged in pallisades

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