Gonococci, like meningococci, cause disease only in humans. The organism is usually transmitted sexually. Newborns can be infected during birth. Because gonococci are quite sensitive to dehydration and cool conditions, sexual transmission favors their survival. Gonorrhea is usually symptomatic in men but often asymptomatic in women. Genital tract infections are the most common source of the organism, but anorectal and pharyngeal infections are important sources as well.
Pili constitute one of the most important virulence factors because they mediate attachment to mucosal cell surfaces and are antiphagocytic. Piliated gonococci are usually virulent, whereas nonpiliated strains are avirulent. Two virulence factors in the cell wall are endotoxin (lipooligosaccharide, LOS) and the outer membrane proteins. The organism’s IgA protease can hydrolyze secretory IgA, which could otherwise block attachment to the mucosa. Gonococci have no capsules.
The main host defenses against gonococci are antibodies (IgA and IgG), complement, and neutrophils. Antibody-mediated opsonization and killing within phagocytes occur, but repeated gonococcal infections are common, primarily as a result of antigenic changes of pili and the outer membrane proteins.
Gonococci infect primarily the mucosal surfaces (e.g., the urethra and vagina). From the mucosal site, bacteria can enter the bloodstream and cause disseminated disease. Certain strains of gonococci cause disseminated infections more frequently than others. The most important feature of these strains is their resistance to being killed by antibodies and complement.
The occurrence of a disseminated infection is a function not only of the strain of gonococcus but also of the effectiveness of the host defenses. Persons with a deficiency of the late-acting complement components (C6–C9) are at risk for disseminated infections, as are women during menses and pregnancy. Disseminated infections usually arise from asymptomatic infections, indicating that local inflammation may deter dissemination.
