Neisseria

Neisseria is a genus of Gram-negative, nonmotile diplococci within the family Neisseriaceae. Most species inhabit the human upper respiratory tract as commensals, though several are notable pathogens. The best known members are Neisseria gonorrhoeae and Neisseria meningitidis, which cause gonorrhea and meningococcal disease, respectively. The genus also includes several nonpathogenic commensals such as Neisseria lactamica and Neisseria sicca.

They are small, oxidase-positive, catalase-positive bacteria that are aerobic or facultatively anaerobic. They appear as kidney-shaped diplococci that may be found inside neutrophils. They ferment carbohydrates, with N. gonorrhoeae fermenting glucose only, and N. meningitidis fermenting glucose and maltose.

Neisseria colonize mucosal surfaces of humans and are transmitted in different ways depending on the species. N. gonorrhoeae is primarily spread by sexual contact; N. meningitidis is spread through respiratory droplets and close contact. Carriage rates vary by age and population and are often asymptomatic.

In disease, N. gonorrhoeae causes gonorrhea, a sexually transmitted infection that can involve the urethra, cervix, pharynx, and rectum, and may disseminate. N. meningitidis can cause meningitis and septicemia; capsule, pili, and outer membrane proteins contribute to virulence, and IgA protease aids mucosal invasion.

Laboratory identification relies on Gram stain of appropriate specimens, oxidase reaction, and culture on selective media such as Thayer-Martin agar. Carbohydrate utilization tests and molecular methods help speciate. Antibiotic resistance is a concern and treatment depends on the species and local guidelines; meningococcal disease is typically treated with third-generation cephalosporins, while gonococcal infections are treated per current guidelines. Vaccines exist for meningococcal disease targeting several serogroups.

Neisseria is placed in the Neisseriaceae family, order Neisseriales, class Betaproteobacteria.