The microorganism that causes gonorrhea is a bacterium named Neisseria gonorrhoeae. It is a Gram-negative diplococci bacterium that primarily infects the mucosal lining of the urogenital tract but can also affect the mucosa of the nose, throat, rectum, and eyes. Neisseria gonorrhoeae is an obligate human pathogen and is transmitted mainly through vaginal, oral, or anal sex. This bacterium has a unique ability to evade the immune system by varying its surface proteins, allowing for repeated infections. It is the sole bacterial species responsible for the sexually transmitted infection known as gonorrhea.