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Corynebacterium diptheriae

  • Slender, non-sporing, non-capsulated, non-motile, non-acid fast, gram + bacilli, 3 x 0.3mm
  • Club shaped swelling at one or both ends
  • Chinese letter pattern
  • Metachromatic granules (volutin, Babes Ernst, polymetaphosphate, polar bodies) 
A. Cultural Characteristic:
  1. Aerobe, facultative anaerobe, temp : 37°c
  2. Growth improved by serum/blood
    1. LSS             
    2. KTBA (0.3% -0.4% potassium tellurite); Macleod, Hoyle’s, Tinsdale
      Biotypes: Mitis, intermedius, gravis
Character Gravis Intermedius Mitis
Morphology Uniformly stained Irregularly stained highly pleomorphic Pleomorphic
Colony Daisy head Frog’s egg Poached egg
Hemolysis sheep RBC Weakly HL NHL ß-HL
Growth in broth Pellicle, granular deposit, no turbidity Uniform turbidity Granular deposit Uniform turbidity
Fermentation of starch/glycogen + - -
Phages types 14 3 4
Serotypes 13 4 40
Toxigenic strains 100% 95-99% 80-85
B. Biochemical Reactions:
  1. Ferments glucose, maltose acid no gas
  2. Does not ferment lactose, mannitol, trehalose
  3. Hiss’s serum peptone water (calf, rabbit serum) (ox, sheep not used) 
C.  Susceptibility to physical and chemical agents:
  1. Killed at 58°C, 10min ; commonly used disinfectants
  2. Resistant to drying (alive for weeks in dust/fomites)
D. Antigenic Structure:
  1. Heat labile type specific protein antigens (K) 
E.  Bacteriophage Typing:
  1. Set of 22 bacteriophages
F.  Toxin Production:
  1. Exotoxin, heat labile protein; 61,150 daltons ; 2 parts; A: 21,150 & B:40,000; A: active; B: binding
  2. Inhibits polypeptide chain elongation by blocking the activity of EF2
  3. When treated with formalin? Toxoid formed
  4. Source of toxin: Park William strain (PW 8)
  5. ß phage codes for tox gene: Lysogenic strains produce toxin. Optimum iron concentration: 0.1 mg/l required for toxin production
G. Pathogenicity:
  1. Person to person by nasopharyngeal secretions
  2. Cases, carriers (nasal carriers)
  3. Children susceptible after 3-6 months of age
  4. IP: 3-4 days
  5. Pseudomembrane: cell necrosis, inflammatory response, necrotic material
  6. Faucial: commonest
    a.  Other types- Laryngeal /Nasal/Otitic/Conjunctival/Genital/Cutaneous               
  7. Based on clinical severity classified as         
  8. Malignant/ hypertoxic
  9. Septic
  10. Hemorrhagic
H. Complications:
  1. Asphyxia
  2. Acute circulatory failure due to myocarditis
  3. Post diphtheritic paralysis (palatine, ciliary)
  4. Septic (pneumonia, otitis media) 
I.   Laboratory Diagnosis:
  1. Don’t wait for laboratory diagnosis
  2. Control measures, epidemiological
  3. Swab two-Albert’s & Gram staining
    a.  LSS /KTBA/ BA
  4. Growth : Gram and Albert’s staining
  5. Biochemical reactions
  6. Toxigenicity tests
In vivo In vitro
Sub cutaneous Elek’s gel precipitation
Intra dermal tissue culture test, LA, ELISA

J.   Schick Test:
  1. In-vivo toxin neutralization
  2. 0.2ml I/D MLD (LT) forearm
  3. Heat inactivated (RT) forearm
Type of reactions Toxin Toxoid Interpretation
  36hrs. 120hrs. 36hrs. 120hrs.  
Negative - - - - Immune & non H.S
Positive + + - - Susceptible & non H.S
Pseudo reaction + - + - Immune & H.S
Combined + + + - Non immune & H.S
K. Active Immunisation
  1. Prophylaxis: Purified toxoid, aluminum precipitated
  2. DPT: 6,10,14 wks , 16-24 months, DT 5-6 yrs age
L.  Passive Immunisation
  1. S/C 500-1000 units ADS
1.  Combined
  1. ADS one arm; diphtheria toxoid other arm
Culture medium for leptospira is (AIIMS May 09)
A. Korotkoff             
B. Becker         
C. Tinsdale              
D. Ludlum’s

Ans. A. Korotkoff
All of the following are culture media for C. diphtheria, except-
A. Loeffler’s serum slope          
B. Tinsdale medium         
C. Macleod’s medium          
D. Ludlam’s medium


M.  Treatment:
1. Antitoxin-Moderate cases: 2000 units I/M
  1. Serious cases: 50,000 units I/V
2.  Antibiotics
  1. Penicillin for eradication from throat,
  2. Erythromycin for carriers

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