Corynebacterium diphtheriae is a bacterium that causes diphtheria, a serious respiratory illness. It is a gram-positive, rod-shaped organism that can produce a toxin, leading to severe throat inflammation and the formation of a thick membrane in the throat. This can obstruct breathing and may result in complications if not treated promptly. The bacterium is primarily spread through respiratory droplets from an infected person. Vaccination with the diphtheria vaccine is crucial for prevention, as it helps the immune system recognize and fight the bacteria. Early diagnosis and treatment with antibiotics are essential to manage the infection effectively.