Corynebacterium diphtheriae is a gram-positive, non-motile bacillus responsible for diphtheria, characterized by club-shaped morphology and the presence of metachromatic granules. The virulence factor, diphtheria toxin, mediates the disease's symptoms, which include respiratory issues and systemic complications due to toxin spread, while diagnosis involves culture and biochemical tests. Treatment includes antitoxin and antibiotics, with vaccination using diphtheria toxoid being crucial for prevention.

1. GRAM POSITIVE BACILLI
CORYNEBACTERIUM DIPHTHERIAE
Prabhakar Singh Patel
(Assistant Lecturer)
SINPS, Lucknow
All Paramedical, Nursing and MBBS Courses

2. CORYNEBACTERIUM
Corynebacteria are gram-positive, non-capsulated,
nonsporing, non-motile rods. They are irregularly stained and
frequently show club-shaped swellings (Greek word koryne,
meaning club).
Corynebacterium diphtheriae, the causative agent of
diphtheria is the most important species pathogenic to man;
other species are occasionally pathogenic, such as C. ulcerans
and C. pseudotuberculosis.

3. CORYNEBACTERIUM DIPHTHERIAE
Corynebacterium diphtheriae is club-shaped, irregularly stained gram-
positive pleomorphic rod that typically shows two characteristic
features:-
1. Chinese letter or cuneiform arrangement: They appear as V- or
L-shaped in smear, because the bacterial cells divide and daughter
cells tend to lie at acute angles to each other. This type of cell
division is called snapping type of division.

4. 2. Metachromatic granules: They are present at ends or poles of the
bacilli (also called polar bodies or Babes-Ernst bodies or volutin
granules). They are storage granules of the organism, composed of
polymetaphosphates. Granules are well developed on enriched media,
such as blood agar or Loeffler's serum slope.

5. VIRULENCE FACTORS
CORYNEBACTERIUM DIPHTHERIAE
Diphtheria Toxin:-
Diphtheria toxin (DT) is the primary virulence factor responsible for
diphtheria.
 The toxin is synthesized in precursor form of molecular weight 58,700
Da (Daltons) containing a polypeptide made up of 535 amino acids.
 Toxin has two fragments; A (active) and B (binding) of molecular
weight 21,500 and 37,200 Da respectively.
 Fragment B is the binding fragment which binds to the host cell
receptors (such as epidermal growth factor) and helps in entry of
fragment A.
 Fragment A is the active fragment, gets internalized into the cell and
then acts by the mechanism given below.

6. Mechanism of Diphtheria Toxin
• Fragment A is the active fragment, which causes ADP ribosylation of
elongation factor 2 (EF-2) → leads to inhibition of EF-2 → leads to
inhibition of translation step of protein synthesis.

7. Factors Regulating Toxin Production
• Phage coded
• Iron concentration
• DT repressor gene
• Biotypes
• Other species- C. ulcerans and C. pseudotuberculosis.

8. Pathogenicity and Clinical Manifestations
CORYNEBACTERIUM DIPHTHERIAE
Pathogenesis of diphtheria is toxin mediated.
Diphtheria is toxemia but never a bacteremia.
Bacilli are noninvasive, present only at local site (pharynx), secrete the
toxin which spreads via bloodstream to various organs.
It is the toxin which is responsible for all types of manifestations including
local (respiratory) and systemic complications (except the skin lesions,
which is caused due to the organism, not toxin).
Respiratory Diphtheria
Cutaneous Diphtheria
Systemic Complications

9. Respiratory Diphtheria
• This is the most common form of diphtheria. Tonsil and pharynx (faucial
diphtheria) are the most common sites followed by nose and larynx.
Incubation period is about 3-4 days.
Faucial diphtheria
Extension of pseudomembrane
Bull-neck appearance

10. Faucial Diphtheria
Diphtheria toxin elicits an inflammatory response, that leads to
necrosis of the epithelium and exudate formation
• This leads to formation of mucosal ulcers, lined by a tough leathery
greyish white pseudomembrane coat; composed of an inner band of
fibrin surrounded by neutrophils, RBCs and bacteria.
• It is so named as it is adherent to the
mucosal base and bleeds on removal,
in contrast to the true membrane which
can be easily separated.

11. Extension of Pseudomembrane
In severe cases, it may extend into the larynx and bronchial airways,
which may result in fatal airway obstruction leading to asphyxia. This
mandates immediate tracheostomy.

12. Bull-Neck Appearance
It is characterized by massive tonsillar swelling and neck edema.
Patients present with foul breath, thick speech, and stridor (noisy
breathing).

13. Cutaneous Diphtheria
It presents as punched-out ulcerative lesions with necrosis, or rarely
pseudomembrane formation; most commonly occurs on the extremities.

14. Systemic Complications
Polyneuropathy and myocarditis are the late toxic manifestations of
diphtheria, occurring after weeks of infection. Other complications of
diphtheria include pneumonia, renal failure, encephalitis, cerebral infarction,
and pulmonary embolism.
Neurologic manifestations: It is a toxin mediated non-inflammatory
demyelinating disorder; presented with-
• Cranial nerve involvement
• Peripheral neuropathy
• Ciliary paralysis
CILIARY PARALYSIS

15. ARRHYTHMIAS DILATED CARDIOMYOPATHY
Myocarditis: It is typically associated with arrhythmias and
dilated cardiomyopathy.

16. LABORATORY DIAGNOSIS
Specimen Collection:-
A PORTION OF MEMBRANE THROAT SWAB

17. DIRECT SMEAR
Gram-stain: Club shaped
gram-positive bacilli with
Chinese letter arrangement.
Albert's stain: Green bacilli
with bluish black metachromatic
granules.

18. CULTURE MEDIA
Enriched Medium:-
Loeffler's Serum Slope
Chocolate Agar
Blood Agar

19. Selective Medium:
Potassium Tellurite Agar Tinsdale Medium

20. BIOCHEMICAL TESTS
 Hiss's serum sugar media: Ferments glucose, maltose and /
or starch
 Urease test negative
Urease test

21. Diphtheria Toxin Demonstration
In Vivo Tests (Guinea Pig Inoculation): Subcutaneous and
Intracutaneous Tests

22. In vitro tests
Elek's gel precipitation test Detection of tox gene-by PCR

23. Detection of toxin-by ELISA or ICT Cytotoxicity on cell lines

24. TREATMENT
Treatment should be started immediately on clinical suspicion of
diphtheria.
Antidiphtheritic serum or ADS (antitoxin)
Antibiotics:-
 Penicillin or Erythromycin is the drug of choice.

25. Vaccination
Active immunization is done with diphtheria toxoid as it induces antitoxin
production in the body.
Types of Vaccine:-
Single Vaccine: Diphtheria toxoid (alum or formal precipitated)
Combined vaccine: Various vaccines available are:
 DPT: Contains DT (diphtheria toxoid), Pertussis. (whole cell) and TT
(tetanus toxoid}
 DaPT: Contains DT, TT and acellular pertussis (Ap)
 DT: Contains DT and TT
 dT: Contains TT and adult dose diphtheria toxoid (d)
 Pentavalent Vaccine: DPT can also be given along with hepatitis B and
Haemophilus influenzae type b.

26. Diphtheria Vaccines

28. Reference
1. J. G. Collee, James Elvins McCartney, and Thomas J. Mackie (1996); Mackie &
Mccartney Practical Medical Microbiology.
2. Apurva S Sastry, Sandhya Bhatt (2019); Essential of medical microbiology.
3. Apurva S Sastry, Sandhya Bhatt (2022); Essential of applied microbiology for nurses.
4. Anmol Chaudhary; Shivlal Pandey (2023); Corynebacterium Diphtheriae,
https://www.ncbi.nlm.nih.gov/books/NBK559015/
5. National Immunization Schedule