N. meningitidis, and apathogenic Neisseria species

Question 1

General Features and habitat of N. Meningitidis

Answer 1

Gram – (diplococci)

Habitat- human nasopharynx (5-10% are asymptomatic carriers)

Fastidious- very sensitive (dryness, heat, disinfectant, antibiotics), not easily growing

Question 2

Biochemical Properties of N. Meningitidis

Answer 2

Oxidase +

IgA protease

Maltose and Glucose fermentation (main difference between N. gonorrhea)

Polysaccharide capsule- inhibit phagocytosis (12 serotypes- A,B,C,X,Y,Z,W-135,H,I,K,L) Type “B” is most lethal- molecular mimicry (identical to E. coli K1 capsular Ag)

Fimbriae (pili) and outer membrane proteins (Omp) for adherence to epithelium

Question 3

Pathogenesis of N. Meningitidis

Answer 3

Transmitted by respiratory droplets (common in dormitory, army units)

Sickle cell and asplenic patients at higher risk of infection (like Strep. pneumoniae)

Late complement deficiency (C5-C9) in patients increase susceptibility to Neisseria

Fimbriae (pili) allow the attachment to mucosal surfaces and inhibits phagocytosis

Fimbriae demonstrate many antigenic variations (by genetic rearrangement)-
this will enable to avoid the immune system response

Question 4

Clinical Features of N. Meningitidis

Answer 4

Lipooligosaccharides (LOS) Endotoxin of cell wall (“envelope”) causes inflammation
Bacteria colonize the pharynx can spread in blood (bacteremia)
After spreading in blood, bacteria can go into the CNS.
LOS on cell membrane are overproduced in that they envelop the surface area of the bacteria and blebbing off.
LOS blebs cause massive inflammatory response with meningitis and sepsis 


Permeability of capillaries increases (inflammation) leading to hypovolemic shock

Petechial rash (from Thrombocytopenia) progress to purpura then ecchymosis
and later to DIC (this is a rapid decline that will eventually cause death)

Waterhouse-Friederischsen syndrome- hypovolemia induces vasoconstriction that will lead to necrosis of adrenal glands (this will also eventually cause death)

Question 5

Diagnosis of N. Meningitidis

Answer 5

Fastidious- grow on Chocolate agar with 5% CO2 (hemoculture is obligatory)

Thayer Martin medium- A.K.A VPN agar (Vancomycin Polymyxin Nystatin)

Latex agglutination- rapid test for capsular Ag (not used in N. gonorrhea- no capsule)

Light microscope- using Gram stain or methylene blue dye (fast staining technique)

Question 6

Treatment of N. Meningitidis

Answer 6

Ceftriaxone (empirically)

Question 7

Prevention of N. Meningitidis

Answer 7

Vaccine contains polysaccharide capsule- for A, C, W, Y serotypes
And another vaccine for serotype B

Prophylaxis Rifampicin or Ciprofloxacin - used for prevention to people who’ve been in close contact

Question 8

Apathogenic Neisseria

Answer 8

N. sicca, 
N. subflava, 
N. flavescens, 
N. mucosa, 
N. pharyngitidis, 
N. lactamica

Question 9

Features of apathogenic Neisseria

Answer 9

General features: Gram negative, aerobic, oxidase positive.

Habitat: normal members of the oral and nasopharyngeal bacterial flora (N. pharyngitidis, A.K.A pharyngococci).

Rarely opportunistic pathogens: respiratory tract infections, endocarditis or conjunctivitis (in case of N. lactamica for example).

Cultivation: easier than pathogenic Neisseria, normal media and ferment several sugars.