Neisseria, a gram-negative diplococcus, consists of two pathogenic species: N gonorrhoeae (gonococcus), which causes gonorrhea, and N meningitidis (meningococcus). Other non-pathogenic species exist. Humans are the only host for gonococcus.

N. gonorrhoeae is an obligate human colonizer that cannot survive outside of its host. Infections spread with direct mucosal contact (genital-genital, rectal-genital, genital-rectal). Pharyngeal gonorrhea is acquired by receptive oral sex, fellatio being more efficient that cunnilingus at transmission. The pharynx may also act as a reservoir of infection, thus facilitating ongoing transmission between partners following oral sex. Neonates of infected mothers may acquire the infection when passing through the birth canal. Disseminated gonococcal infections (DGI) occur with hematogenous spread to other anatomic sites such as the skin, joints, liver, heart, or brain.