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Pathogenic Neisseriae: Gonorrhea, Neonatal Ophthalmia and Meningococcal Meningitis (page 1)
(This chapter has 7 pages)
© Kenneth Todar, PhD
The Neisseriaceae are a family of Beta Proteobacteria
consisting of Gram-negative
bacteria from fourteen genera (Bergey's 2005), including Neisseria,
Chromobacterium, Kingella, and Aquaspirillum. The
contains two important human pathogens, N. gonorrhoeae and N.
meningitidis. N. gonorrhoeae
causes gonorrhea, and N.
is the cause of meningococcal meningitis. N. gonorrhoeae
have a high prevalence and low mortality, whereas N. meningitidis
infections have a low prevalence and high mortality.
gonorrhoeae infections are acquired by sexual
and usually affect the mucous membranes of the urethra in males and the
endocervix and urethra in females, although the infection may
to a variety of tissues. The pathogenic mechanism involves the
of the bacterium to nonciliated epithelial cells via pili
the production of lipopolysaccharide endotoxin. Similarly, the
of Neisseria meningitidis is highly toxic, and it has an
virulence factor in the form of its antiphagocytic capsule. Both
produce IgA proteases which promote virulence. Many normal individuals
may harbor Neisseria meningitidis in the upper respiratory
but Neisseria gonorrhoeae is never part of the normal flora
is only found after sexual contact with an infected person (or direct
in the case of infections in the newborn).
In the vocabulary of
the public health and medical
N. gonorrhoeae is often referred
to as the "gonococcus", while N.
meningitidis is known as the "meningococcus", and one form of the
it causes is called meningococcemia.
Figure 1. Left: Neisseria
gonorrhoeae Gram stain of pure culture; Right: Neisseria
Gram stain of a pustular exudate.
Neisseria gonorrhoeae is a
Gram-negative coccus, 0.6 to 1.0
in diameter, usually seen in pairs with adjacent flattened sides
1 Left and Fig 2 below). The organism is frequently found
in polymorphonuclear leukocytes (neutrophils) of the gonorrhea pustular
exudate (Figure 1 Right). Fimbriae or pili, which play a major role in
extend several micrometers from the cell surface (Figure 2 below).
Figure 2. Neisseria
gonorrhoeae possesses a typical Gram-negative outer
membrane composed of proteins, phospholipids, and lipopolysaccharide
However, neisserial LPS is distinguished from enteric LPS by its
basal oligosaccharide structure and the absence of repeating O-antigen
subunits. For these reasons, neisserial LPS is referred to as lipooligosaccharide
(LOS). The bacterium characteristically releases outer membrane
fragments called "blebs" during growth. These blebs contain LOS
probably have a role in pathogenesis if they are disseminated during
course of an infection.
is a relatively fragile organism, susceptible
to temperature changes, drying, uv light, and other environmental
Strains of N. gonorrhoeae are fastidious and variable in their
so that media containing hemoglobin, NAD, yeast extract and other
are needed for isolation and growth of the organism. Cultures are grown
at 35-36 degrees in an atmosphere of 3-10% added CO2.