Corynebacterium Diphtheria
INTRODUCTION:
- Gram-positive
- Nonmotile rods
- High G+C (guanine + cytosine) content
MORPHOLOGY:
- Thin, slender, non sporing
- Appear in short chains (“V” or “Y” configurations) or in clumps resembling “Chinese letters”.
- Metachromatic granules
- intracytoplasnic inclusions
- Give Club shape to diptheria
- Present of at one or both ends
- Also called volutin or babes-Ernst granules.
- Special stains like albert [ malachite green & toludine blue], neisser or polychrome methylene blue are used for staining.
There are 3 biotypes-
- gravis
- intermedius
- mitis.
With albert stain
- The bacilli look green
- Metachromatic granules look bluish black
CULTURAL CHARACHTERSTICS:
- Media enriched with blood serum or egg.
Hiss serum water:
- Liquid media containing serum- growth seen as turbidity and pellicle formation.
Loefflers serum slope:
- Rapid growth 6-8 hours-small circular, white or creamy and glistening.
Tellurite blood agar:
- Potassium tellurite 0.04%- act as selective media
- Black colonies due to reduction of tellurite to tellurium.
- Colonies appears after 48 hrs.
Tinsdale agar
- Contains sheep’s blood, bovine serum, cystine and potassium tellurite is selective medium.
- Brown halo surrounding the colony is differentiating feature.
BIOCHEMICAL REACTION:
- Ferment glucose and maltose with acid but no gas.
- Don’t ferment lactose, mannitol or sucrose
- Don’t hydrolyse urea or form phosphatase.
- Gelatin is not liquified
Diphtheria Toxin
- Heat Labile Polypeptide exotoxin
- Production iron concentration dependent.
- The optimum level of iron for toxin production is 0.1 mg per liter
- While a concentration of 0.5 mg per litre inhibits the formation of toxin.
Made up of two fragments:
Fragment B
- Binding
Fragment A
- Enzymatic activity inactivating elongation factor (EF-2) in presence of NAD.
- Inhibit protein synthesis.
- Synthesized in precurser form (inactive) in the pseudomembranous lesion.
- Lysogenic conversion:Toxigenic conversion of toxphenotype to tox + phenotype
- ‘ParkWilliam 8’ Strain:strain almost universally used for toxin production
Exotoxin is also produced by
- C. ulcerans
- C. pseudotuberculosis.
- Both tox + and tox-strains are infectious.
- Toxin is phage mediated
Local effects:
- Bacilli remain confined to the site of entry .
- Multiply and produce toxin.
- Toxin causes local necrotic changes along with superficial inflammatory reactions
- The necrosed epithelium together with fibrinous exudates, leucocytes, erythrocytes and bacteria constitute pseudomemebrane.
- Which makes problem in swallowing.
Systemic effects:
- Toxin diffuses to blood streams and causes toxemia
- The toxin has got affinity for cardiac muscle, adrenals and nerve endings.
- It acts systematically on the cells of these tissues
- The bacilli themselves do not play any part in the systemic effects because they neither penetrate in to the tissue nor pass into blood stream producing bacteremia.
Exam Question
INTRODUCTION:
- Gram-positive
MORPHOLOGY:
- Appear in short chains (“V” or “Y” configurations) or in clumps resembling “Chinese letters”.
- Metachromatic granules
- Give Club shape
- Present of at one or both ends
- Also called volutin or babes-Ernst granules.
- Special stains like albert [ malachite green & toludine blue], neisser or polychrome methylene blue are used for staining.
CULTURAL CHARACTERISTICS:
Tellurite blood agar:
- Black colonies due to reduction of tellurite to tellurium.
- Colonies appears after 48 hrs.
Tinsdale agar
- Brown halo surrounding the colony is differentiating feature.
Diphtheria Toxin
- Heat Labile Polypeptide exotoxin
- Production iron concentration dependent.
- Toxin is phage mediated
- Have both local and systemic effect.
Don’t Forget to Solve all the previous Year Question asked on Corynebacterium Diphtheria
