structural:reformatting, quality:correction
Identification

To identify C. diphtheriae, a Gram stain is performed to show Gram-positive, highly pleomorphic organisms often looking like Chinese letters. Stains like Albert's stain and Ponder's stain are used to demonstrate the metachromatic granules formed in the polar regions. The granules are called polar granules, Babes Ernst granules or volutin granules. An enrichment medium, such as Löffler's medium, is used to preferentially grow C. diphtheriae. After that, a differential plate known as tellurite agar, allows all Corynebacteria (including C. diphtheriae) to reduce tellurite to metallic tellurium. The tellurite reduction is colorimetrically indicated by brown colonies for most Cornyebacterium species or by a black halo around the C. diphtheriae colonies. The organism produces catalase but not urease, which differentiates it from Corynebacterium ulcerans. C. diphtheriae does not produce pyrazinamidase which differentiates from Corynebacterium striatum and Corynebacterium jeikeium.