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Pathogenic Neisseriae: Gonorrhea, Neonatal Ophthalmia and Meningococcal Meningitis (page 1)

(This chapter has 7 pages)

© Kenneth Todar, PhD

Neisseria meningitidis scanning EM

Introduction

The Neisseriaceae are a family of Beta Proteobacteria consisting of Gram-negative aerobic bacteria from fourteen genera (Bergey's 2005), including Neisseria, Chromobacterium, Kingella, and Aquaspirillum.  The genus Neisseria contains two important human pathogens, N. gonorrhoeae and N. meningitidis. N. gonorrhoeae causes gonorrhea, and N. meningitidis is the cause of meningococcal meningitis. N. gonorrhoeae infections have a high prevalence and low mortality, whereas N. meningitidis infections have a low prevalence and high mortality.

Neisseria gonorrhoeae infections are acquired by sexual contact and usually affect the mucous membranes of the urethra in males and the endocervix and urethra in females, although the infection may disseminate to a variety of tissues. The pathogenic mechanism involves the attachment of the bacterium to nonciliated epithelial cells via pili and the production of lipopolysaccharide endotoxin. Similarly, the lipopolysaccharide of Neisseria meningitidis is highly toxic, and it has an additional virulence factor in the form of its antiphagocytic capsule. Both pathogens produce IgA proteases which promote virulence. Many normal individuals may harbor Neisseria meningitidis in the upper respiratory tract, but Neisseria gonorrhoeae is never part of the normal flora and is only found after sexual contact with an infected person (or direct contact, in the case of infections in the newborn).

In the vocabulary of the public health and medical microbiologist,  N. gonorrhoeae is often referred to as the "gonococcus", while N. meningitidis is known as the "meningococcus", and one form of the disease it causes is called meningococcemia.

Figure 1. Left: Neisseria gonorrhoeae Gram stain of pure culture; Right: Neisseria gonorrhoeae Gram stain of a pustular exudate.

Figure 2. Neisseria gonorrhoeae

Neisseria gonorrhoeae possesses a typical Gram-negative outer membrane composed of proteins, phospholipids, and lipopolysaccharide (LPS). However, neisserial LPS is distinguished from enteric LPS by its highly-branched 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 and probably have a role in pathogenesis if they are disseminated during the course of an infection.

N. gonorrhoeae is a relatively fragile organism, susceptible to temperature changes, drying, uv light, and other environmental stresses. Strains of N. gonorrhoeae are fastidious and variable in their cultural requirements, so that media containing hemoglobin, NAD, yeast extract and other supplements are needed for isolation and growth of the organism. Cultures are grown at 35-36 degrees in an atmosphere of 3-10% added CO₂.