This document summarizes the characteristics and pathogenicity of Corynebacterium diphtheriae, which causes diphtheria. It notes that C. diphtheriae appears as slender, gram-positive rods that can have club-shaped ends and contain metachromatic granules. Infection typically occurs in the upper respiratory tract, where the bacteria's toxin causes a pseudomembrane and systemic effects. Transmission is through droplets or direct contact. Immunization with diphtheria toxoid vaccine provides protection against the disease.

1. BY : Dr GAURAV MATHUR

2.  Slender Gram-positive rods, pleomorphic; easily
decolousised;
 0.6-0.8μ diameter and 3-6 μ length;
 Irregular swelling at one or both ends (‘club
 shaped’);
 Non-capsulate, Non-sporing and nonmotile
 Granules containing polymetaphosphate are seen
in the cells;
 Take up bluish purple color against lightly stained
cytoplasm, when stained with Loeffler’s Methylene
Blue, and hence called ‘Metachromatic granules’;
 • Also called, ‘volutin granules’ or ‘Babes Ernst
 granules’;
 • They are often situated at poles- ‘polar bodies

3.  Special stains for demonstrating the granules :
 – Albert’s stain
 – Neisser’s stain
 – Ponder’s stain
 • The bacilli are arranged in
 pairs, palisades or small
 groups; the bacilli lie at
 various angles to each other,
 resembling the letters, V or L;
 • This is called,
“Chinese letter
 pattern” or “cuneiform
 pattern”;

4.  • Blood agar
 • Loeffler’s serum slope
 • Tellurite blood agar
 • Tinsdale’s medium (cystine added to
tellurite containing agar)

5.  • Blood agar : small,
 granular and gray with
 irregular edges;
 Hemolysis may or may not present;
 Loeffler’s serum slope:
 – Very rapid growth;
 – Colonies in 6-8 hrs
 – Initially circular white
 opaque colonies and
 acquire yellowish tint on
 incubation

6.  Tinsdale’s medium (also contain cystine in
 addition to tellurite):
 – Grey black colonies with
 dark brown haloes
 indicate C.diphtheriae

7.  • Ferment- glucose, galactose, maltose and
 dextrose; but not lactose, sucrose, mannitol;
 • Proteolytic activity is absent;
 • Do not hydrolyse urea;
 • Do not form phosphatase;
 • Produce cystinase (halo on Tinsdale’s
medium)

8.  The pathognomonic effects are due to the Toxin
Toxin is a protein
Two fragments, A and B;
 Fragment B : binds to a cell surface receptor
 and helps in transport of toxin into the cell;
 • After entering the cell, A subunit is released ;
 • A subunit catalyses the transfer of ‘adenosine
diphosphate ribose (ADPR)’
 • ADPR binds with the elongation factor EF 2
 • “ADPR-EF2” complex is inactive protein
 synthesis stops abruptly necrotising and
 neurotoxic effects of the toxin;

9.  • Commonest site of infection: Upper
respiratory tract (fauces, larynx,nose)
 • Ocassionally, other cutaneous or
 mucocutaneous areas ( otitic/conjunctival/
 genitovulval/vaginal/ prepucial/skin)
 • Faucial diphtheria is the commonest type;
 • Sore throat is frequently the presenting
 symptom;

10.  • The toxin causes local necrotic changes;
 • The resulting fibrinous exudate, together
with
the epithelial cells, leucocytes, erythrocytes
and bacteria constitute : “pseudomembrane”
 • Any effort to remove it will tear off
capillaries
beneath it and cause bleeding;
 • Mechanical complications are due to
pseudomembrane and systemic effects are
due to the toxin

11.  • The toxin is absorbed systemically and
damages heart muscle, liver, adrenals etc.
 Nontoxigenic strains can also produce local
disease but systemic effects are absent
 • Incubation period : usually 3-4 days;
 • Acute infection : in the form of –
 – Membranous tonsillitis
 – Nasal infection
 – Laryngeal infection
 – Skin infection –uncommon

12.  Characteristic feature is :
 ‘wash –leather’ eleveted
 greyish greeen
 membrane in the tonsils
 with a well defined
Edge surrounded by a
zone of
inflammation;

13.  CLASSIFICATION BASED ON CLINICAL
SEVERITY
 • Malignant or hypertoxic:
 – ‘Bull neck’ due to marked
adenitis in neck;
 – Severe toxemia
 – Circulatory failure
 – Death
 – Paralytic squealae in survivors
 • Septic : ulceration, cellulitis and gangrene
 around pseudomembrane;
 • Hemorrhagic: bleeding from the edge of
 pseudomembrane, epistaxis, purpura etc.

14.  • Asphyxia : due to mechanical obstruction
 Emergency tracheostomy may be necessary;
 • Acute circulatory failure
 • Myocarditis
 • Postdiphtheritic paralysis-
 palatine(soft palate) and ciliary ( eye
muscles)
 nerves
 Recovery – spontaneous and complete
 • Septic : pneumonia and otitis media

15.  • Specimens :
 – Swabs from – nose, throat or other
suspected
 lesions;
 • Smear examination: Gram stain
 – shows beaded rods in typical arrangement;
 corynebacteria normally found in throat;
 – Albert’s stain or Neisser’s stain is useful for
demonstrating the granules

16.  • Inoculate on :
 – Loeffler’s serum slope
 – Tellurite blood agar or Tinsdale medium
 – Blood agar
 • In vivo methods:
 – Subcutaneous test
 – Intracutaneous test
 • In vitro methods:
 – Elek’s gel precipitation test
 – Tissue culture test

17.  • In vitro test;
 • A rectangular strip of filter paper is
saturated
 with the diphtheria antitoxin(1000 units/ml);
 • This strip is placed on : agar plate with 20%
 horse serum, while the medium is setting;
 • The cultures to be tested are streaked at
right
 angles to the filter paper strip

21.  Mainly a disease of childhood(pediatrics) in
endemicareas – uncommon below 1st year; peaks
at 5.
 • In nature, C.diphtheriae occurs in the
respiratory tract, in the wounds or in the skin of
the infected
 persons or carriers;
 • Transmission is by-
 – Droplet dissemination from cases or carriers
 – Direct contact
 – Occasionally, fomites

22.  ACTIVE IMMUNISATION
 Two preparations of toxoid are available:
 – Formol toxoid
 – Adsorbed toxoid
 • Formal toxoid : prepared by incubating the
 toxin with formalin for 3-4 weeks;
 • Adsorbed toxoid : purified toxoid is adsorbed
 onto an adjuvant, either aluminium phosphate
 or aluminium hydroxide; this is more
 immunogenic;

23.  • Adsorbed toxoid –given as IM injections
 • Recommended vaccines:
 – As a trivalent preperation : DPT (adsorbed
 Diphtheria/Pertusis/Tetanus)
 – Adsorbed Diphtheria/Tetanus (DT)
 – Adsorbed low dose diphtheria vaccine for
adults (d)
 – Adsorbed Tetanus/low dose diphtheria
vaccine(Td)
 for adults;
 – A quadraple vaccine containing
DPT+inactivated
 polio vaccine is also available;

24. 3 DOSE of DPT at 6 , 10 and 14 week
AND
2 BOOSTER dose at 16-24 month and 5-6 years of
age
TOTAL 5 DOSE– 0.5ml
ROUTE Intramuscular
PASSIVE : Antidiptheric serum
 As an emergency measure when susceptibles are
exposed to infection
 Subcutaneous administration of500-1000 units
of antitoxin orADS(Antidiphtheritic serum);

25.  • Specific measure : prompt administration of
antitoxin to neutralize the circulating toxin;
 • Antibiotics : Penicillin or Erythromycin for
14 days;
 • Complete bed rest;
 • Supportive therapy and treatment of
complications
 • Erythromycin: for treatment of carriers

26. THANK YOU
SEE YOU IN NEXT CLASS