Diphtheria is an acute infectious disease of the mucus membrane or the skin caused by Corynebacterium diphtheriae and Corynebacterium ulcerans. The bacteria that has the following characteristics, it is:

 Aerobic,

 Non-motile,

 Gram-positive,

 Rod shaped,

 Produces toxins

The bacteria can cause inhalational or cutaneous forms of the disease. They can also enter the body through the eyes, ears, or genitals.

The bacteria usually affect the tonsils, throat, nose, skin and very rarely the heart and the nerves. It is a very contagious and potentially life-threatening. It spreads when people are in close contact with discharges from an infected person's mouth, nose, throat, or skin.

Humans are the only reservoir of infection. Communicability may last 4 weeks. Dusts and clothing also may contribute to transmission. The organism can survive up to 6 months in dust and fomites. Diphtheria toxin that is an exotoxin is produced only by strains of C. diphtheriae that are lysogenized with bacteriophages that contain the structural gene for the toxin molecule.