Corynebacterium diphtheriae

Corynebacterium diphtheriae is a pathogenic bacterium that causes diphtheria. It was discovered in 1884. There are four subspecies C. diphtheriae mitis, C. diphtheriae intermedius, C. diphtheriae gravis, and C. diphtheriae belfanti. They all are a little bit different in their colonial morphology and biochemical properties such as the ability to metabolize certain nutrients.

The diphtheria toxin gene is encoded by a bacteriophage which is found in toxigenic strain. A gram stain is performed to show gram-positive, highly pleomorphic organisms with no particular arrangement. Special stains are used to demonstrate the metachromatic granules formed in the polar regions.

For toxin production to happen a low concentration of iron is required. The aporepressor shuts down toxin production when bound to iron. Elek’s test is used to determine whether the organism is able to produce diphtheria toxin or not. Bacterium is sensitive to most antibiotics.