Corynebacterium diphtheriae

Corynebacteria are small, slender, pleomorphic, gram-positive rods& Chinese letters. They are nonmotile, unencapsulated, and do not form spores, containing chromatin granules called volutin granules or Babes- Ernest granules present in cytoplasm and aggregated in the poles of the cells.
Pathogenesis:
Diphtheria is caused by the local and systemic effects of a single exotoxin that inhibits eukaryotic protein synthesis. Diphtheria, caused by C. diphtheriae, is an acute respiratory or cutaneous disease and may be a life-threatening illness, diphtheria is a serious disease throughout the world, particularly in those countries where the population has not been immunized.
Clinical significance
Infection may result in clinical disease which has two forms respiratory and cutaneous or in an asymptomatic carrier state.
1. Upper respiratory tract infection: Diphtheria consists of a strictly local infection, usually of the throat. The infection produces a distinctive thick, grayish, adherent exudate (pseudomembrane) that is composed of cell debris from the mucosa and inflammatory products
2. Cutaneous diphtheria: A puncture wound or cut in the skin can result in introduction of C. diphtheriae into the subcutaneous tissue, leading to a chronic, non healing ulcer with a gray membrane.
Laboratory identification: gram-positive rods& Chinese letters. They are containing chromatin granules called volutin granules or present in cytoplasm and aggregated in the poles of the cells (staining by Albert stain). Most species are facultative anaerobes; grow aerobically on standard laboratory media such as Chocolate & blood agar.