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Corynebacterium diphtheriae : Essentials for MBBS Microbiology
- 1. Corynebacterium diphtheriae “Diphtheria is Toxemiaand Not Bacteremia”
- 2. Objectives • General properties •Virulence • Pathogenesis • Clinical features • Lab Diagnosis • Summary
- 3. General Properties • Aka“Klebs-Loeffler Bacillus” • Non-motile • Aerobic • Gram +ve • Non sporing • Non capsulated
- 4. Virulence • “Diphtheria Toxin” •Main villain of the story • Responsible for the infection • Toxicity and Antigenicity • Special affinity to heart and nerves • Polypeptide chain : A and B fragments “Diphtheria is Toxemia and Not Bacteremia” Protein Synthesis
- 5. Pathogenesis “Diphtheria is Toxemiaand Not Bacteremia” 1. Respiratory Diphtheria 1. Faucial(Pharynx) 2. Nasal 3. Larynx 2. Cutaneous diphtheria : Ulcers 3. Systemic diphtheria 1. Nerves : Palatal Paralysis 2. Myocarditis
- 6. Toxin Damage and necrose theepithelial cells of tonsils and pharynx Forms exudate and ulcers ‘PseudoMembrane’ (Neutrophils, RBCs and Bacteria) Extend into Nose and Larynx Asphyxial Death by Obstruction “Bleeds on Removal”
- 7. Lab Diagnosis Demonstration ofBacteria Demonstration of Toxin • Sample Collection • Throat Swab • Piece of Pseudomembrane • Microscopy • Gram Stain • Albert’s Stain • Culture • Biochemical Identification • In-vivo • Guinea Pig • In-vitro • Elek’s Gel Precipitation Test • Molecular : PCR & ELISA/ICT
- 8. Demonstration of Bacteria Microscopy GramStain +Ve Albert’s Stain “Chinese Letter Arrangement” Metachromatic Granules (Storage Granules)
- 9. Culture Demonstration of Bacteria Loeffler’sSerum Slope Potassium Tellurite Agar Small creamy colonies Black colonies (d/t reduced tellurium)
- 10. Demonstration of Bacteria BiochemicalIdentification • Catalase +ve • Oxidase -ve • Indole -ve • Citrate utilisation test -ve • Urease -ve Outstanding Points • Hiss’s Serum Sugar Media : Glucose Fermentative • Pyrazinamidase -ve
- 11. Demonstration of Toxin In-vivo In-vitro “Elek’sGel Precipitation Test” 1 to 4 (Toxigenic) 5 (Non-Toxigenic) 1 & 2 : Unrelated strain 2 & 3 : Partially related 3 & 4 : Identical Strains Horse Serum Agar
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- 13. Outstanding Points Pentavalent Vaccine(NIS) • Diphtheria • Pertussis • Tetanus • Hepatitis B • Hib Antibiotics ineffective (except for skin lesions) Commensal Corynebacterium k/a Diphtheroids Park-William 8 Strain Antigenicity Active Immunity (6, 10 & 14 wks)
- 14. Summary • ‘Klebs-Loeffler Bacillus’causes Diphtheria • Diphtheria toxin is toxic and Antigenic • Pseudomembrane characterises the disease • Special stain : Albert’s stain • Culture : “Loeffler serum agar” and PTA • Toxin demonstrated by “Elek’s Gel Precipitation Test” • Antitoxin immediately administered if diphtheria is suspected
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