True about corynebacterium diptheriae –
Correct Answer: Toxin production is dependent upon critical concentration of iron
Description: Ans. is 'b' i.e., Toxin production is dependent upon critical concentration of ironPathogenicity of diphtheriao Diphtheria is a toxemia. The bacilli remain confined to the site of entry-, where they multiply and form the toxin.o Toxin causes local necrotic changes and the resulting fibrinous exudate, together with the disintegration and bacteria, constitute the pseudomembrane, which is characteristic of diphtheric infection,o The mechanical complications of diphtheria are due to the membrane, while the systemic effects are due to the toxin.o Toxin is heat labile.o The toxigenicity of the diphtheria bacilli depends on the presence in it of corvnephages (tox +). Nontoxigenic strains may be rendered toxigenic by infecting them with beta phage or some other larger phage. This is known as lysogenic conversion or phage conversion.o C. diphtheriae does not need to be toxigenic to establish localized infection - Jawetz 23rd.'e 214o Systemic manifestations are due to exotoxemia not endotoxemia. Endotoxemia is produced by gram (-)ve organisms, while diphtheria is gram {+) ve.o Toxin acts by inhibiting synthesis of protein.Diphtheria toxino The diphtheria toxin acts by inhibiting protein synthesis. It inhibits polypeptide chain elongation in the presence of nicotinamide adinine dinucleotide (NAD) by inactivating elongation factor, EF - 2.o The diphtheria toxin is a protein which consists of two fragments, A and B.o Both fragments are necessary for the toxic effect:Fragment A - has enzymatic activity' and inhibits protein synthesis by inhibiting the chain elongation by inactivating the elongation factor - 2 (Ef - 2)Fragment B - responsible for binding the toxin to the cells,o Toxin has special affinity for certain tissues such as myocardium, adrenals and nerve endings.o The strain almost universally used for toxin production is the "Park williams 8 strain "o Toxin production is influenced by the concentration of iron in the medium.o 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.
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Microbiology
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