The infection is caused by bacteria called Corynebacterium diphtheriae. An infected person, unless treated with antibiotics, is infectious for two to three weeks. The pseudomembrane is formed from waste products and proteins caused by the toxin secreted by the bacteria. The pseudomembrane sticks to tissues and may obstruct breathing. The toxin itself may travel to the heart, muscle, kidneys, and liver, where it may temporarily or permanently damage these organs.