Catherine Ison and Brian Robertson, Department of Medical Microbiology, Imperial College School of Medicine at St Mary's, London, UK
The genus Neisseria belongs to the family Neisseria-ceae and contains 12 species, of which only N. gonorrhoeae and N. meningitidis are considered primary pathogens. Although these two species share 80% DNA homology they cause diverse types of infections. N. gonorrhoeae causes primarily a mucosal infection of the urogenital tract known as uncomplicated gonococcal infection (UGI). In a few patients, complicated gonococcal infection presents as pelvic inflammatory disease (PID) in women and as epididymitis and prostatitis in men. Disseminated gonococcal infection is rare and presents as septicemia, rash or arthritis. It is more common in women and is associated with strains that are highly susceptible to penicillin and require arginine, hypoxanthine and uracil for growth. N. meningitidis colonizes the mucosa of the upper respiratory tract as a commensal and encapsulated strains can cause systemic infection resulting in meningitis. N. gonorrhoeae and
N. meningitidis are obligate human pathogens and have no other natural reservoir.
Neisseria spp. are gram-negative diplococci, produce cytochrome c (oxidase) and utilize carbohydrates by the oxidative pathway. N. gonorrhoeae utilizes only glucose whereas N. meningitidis utilizes both glucose and maltose. They require complex media for growth and are enhanced by 5-7% carbon dioxide.
The neisserial cell envelope consists of a cytoplasmic membrane, a thin peptidoglycan layer and an outer membrane. The main outer membrane antigens of N, gonorrhoeae and N. meningitidis are listed in Table 1.
N. gonorrhoeae can be divided into serovars dependent on the antigenic specificity of Por which occurs in two types, PIA and PIB. Gonococci belonging to PIA serovars are more susceptible to antibiotics and PIB more resistant. Encapsulated strains
Table 1 Cell wall antigens of Neisseria gonorrhoeae and N. meningitidis
N. gonorrhoeae N. meningitidis
LPS, LOS Cps
Protein I (PI)
Protein III (Pill) Protein II (Pll)
Class 1 Class 2 and 3 Class 4 Class 5 Class I pilin
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