The genus Neisseria comprises gram-negative, oxidase-positive bacteria that characteristically appear under the microscope as pairs of kidney-bean shaped cells, known as diplococci. Within this large genus, two species are major human pathogens: Neisseria gonorrhoeae, which causes the sexually transmitted infection gonorrhoea, and Neisseria meningitidis, a leading cause of bacterial meningitis and septicaemia. Other members of the genus, such as Neisseria sicca and Neisseria lactamica, typically exist as harmless commensals in the upper respiratory tract. Pathogenic species are notoriously fragile, sensitive to drying, and easily destroyed by cold temperatures, meaning they require prompt laboratory processing after collection from a patient.
Neisseria species rely on a suite of structural components to establish infection and evade the host immune response.
Infections caused by pathogenic Neisseria present with distinct clinical pictures depending on the species involved. Neisseria gonorrhoeae primarily infects mucous membranes of the urogenital tract, resulting in purulent urethral discharge in men and endocervical discharge in women, though rectal and pharyngeal infections are also common. Left untreated, it can ascend to cause pelvic inflammatory disease. Conversely, Neisseria meningitidis colonises the nasopharynx and can invade the bloodstream, leading to meningococcal meningitis characterized by a stiff neck, high fever, and altered mental state, or fulminant septicaemia accompanied by a non-blanching purpuric rash and circulatory collapse.
Accurate identification of Neisseria requires meticulous handling of clinical specimens because the bacteria die quickly outside the human body. For suspected gonorrhoea, endocervical or urethral swabs are collected and can be examined under a microscope using a gram stain to look for intracellular gram-negative diplococci within neutrophils. Culture remains the gold standard, requiring enriched media such as Thayer-Martin agar incubated in a carbon dioxide-rich environment. For suspected meningitis, cerebrospinal fluid (CSF) obtained via lumbar puncture is evaluated for elevated protein, lowered glucose, and the presence of organisms on microscopy.
Managing patients with Neisseria infections requires a combination of targeted antimicrobial therapy and strict infection control practices. Confirmed cases of gonorrhoea are treated with recommended antibiotic regimens, such as intramuscular ceftriaxone, alongside partner notification and treatment to prevent reinfection. For suspected meningococcal disease, urgent intravenous antibiotics must be administered immediately without waiting for lab confirmation, as the condition can deteriorate within hours. Midwives and nurses caring for patients with meningococcal meningitis must institute respiratory isolation precautions for the first twenty-four hours of effective treatment to protect other patients and staff.