Neisseria Bacteria: Properties and Pathogens

The genus Neisseria contains two important human pathogens: Neisseria meningitidis and Neisseria gonorrhoeae.
Neisseria meningitidis mainly causes meningitis and meningococcemia, and is the leading cause of death from infection in children in the United States.
Neisseria gonorrhoeae causes gonorrhea, the second most common bacterial disease in the United States, as well as neonatal conjunctivitis and pelvic inflammatory disease.

Neisseriae are gram-negative cocci that resemble paired kidney beans.
Neisseria meningitidis has a prominent polysaccharide capsule that enhances virulence by its antiphagocytic action.
The capsule also serves as an immunogen in the vaccine that induces protective antibodies.
Meningococci are divided into at least 13 serologic groups based on the antigenicity of their capsular polysaccharides.
Five serotypes (A, B, C, Y, and W-135) cause most cases of meningitis and meningococcemia.

Neisseria gonorrhoeae has no polysaccharide capsule but has multiple serotypes based on the antigenicity of its pilus protein.
Gonococci have three outer membrane proteins (proteins I, II, and III), with protein II playing a role in attachment of the organism to cells and varying antigenically.
Gonococci have marked antigenic variation in their pili due to chromosomal rearrangement, with over 100 serotypes known.

Neisseriae are gram-negative bacteria and contain endotoxin in their outer membrane.
The endotoxin of Neisseriae consists of lipooligosaccharide (LOS), in contrast to the lipopolysaccharide (LPS) found in enteric gram-negative rods.

Humans are the only natural hosts for meningococci.
Meningococci are transmitted by airborne droplets and colonize the membranes of the nasopharynx, becoming part of the transient flora of the upper respiratory tract.
Carriers are usually asymptomatic, but the organism can enter the bloodstream and spread to specific sites or be disseminated throughout the body.
Meningococci have four important virulence factors: polysaccharide capsule, endotoxin, immunoglobulin A (IgA) protease, and factor H binding protein.

Moraxella species are gram-negative coccobacillary rods that resemble the diplococcal appearance of Neisseriae.
Moraxella catarrhalis is the major pathogen in this genus, causing otitis media, sinusitis, bronchitis, and pneumonia.
Moraxella catarrhalis is found only in humans and is transmitted by respiratory aerosol.
Trimethoprim-sulfamethoxazole or amoxicillin-clavulanate can be used to treat these infections, and most clinical isolates produce β-lactamase.

Veillonella are Gram-negative bacteria anaerobic cocci, unlike most Bacillota, which are Gram-positive bacteria.
Veillonella are known for their lactate fermenting abilities and are normal bacteria in the intestines and oral mucosa of mammals.
Veillonella have been implicated in cases of osteomyelitis and endocarditis, and Veillonella dispar is the most nitrate-reducing bacterium in the oral cavity.
When Veillonella is responsible for clinical infections in humans, more than 70% of the strains are resistant to penicillin.