Neisseriaceae Flashcards
Important features of Neisseria spp.
(1) Gram (-) diplococci: appear as pairs of kidney-shaped cells when viewed under the microscope.
(2) Oxidase positive: oxidase is used in the electron transport chain.
(3) Fimbriae: for adhesion to host cells and tissues.
(4) IgA protease: degrades IgA
(5) Catalase positive: catalse breaks down hydrogen peroxide into water and oxygen.
Name two culture mediums used for Neisseria spp.
(1) Chocolate agar
(2) Thayer-Martin
What antibiotics is Thayer-Martin agar enriched with?
(1) Vancomycin
(2) Polymyxin
(3) Nystatin
Name an immunodeficiency which associated with increased susceptibility to Neisseria spp.
C5-9 deficiency
Why is Neisseria spp. so effective at evading the immune system?
Antigenic variation of the pili and IgA protease.
Name four bacteria with IgA proteases.
(1) Neisseria gonorrhoeae
(2) Neisseria meningitidis
(3) Haemophilus influenzae
(4) Streptococcus pneumoniae
Which species of Neisseria ferments maltose?
N. meningitidis
What is the first place N. meningitidis colonizes?
Nasopharynx
Which strain of N. meningitidis most commonly causes meningitis?
Type B
Name two genetic defects which increase the risk for N. meningitidis infection.
(1) C5-9 deficiency
(2) Sickle cell disease
Instead of lipopolysaccharides, N. meningitidis has ________.
lipooligosaccharides
What organism is most associated with meningitis with a petechial rash?
Neisseria meningitidis
[Image]
How is N. meningitidis transmitted?
Respiratory route, saliva
Briefly discuss N. meningitidis virulence factors.
(1) Polysaccharide capsule
Enables the bacteria to evade phagocytosis by PMNs.
It also protects against soluble immune effector mechanisms in serum.
(2) Pili, surface proteins Opa and Opc
These facilitate the attachment of the bacteria to host cells, particularly in the nasopharynx.
(3) Endotoxin
The lipooligosaccharide endotoxin causes fever, septic shock, and DIC by triggering a strong inflammatory response.
(4) IgA protease
(5) Transferrin binding proteins: enable the bacterium acquire iron from host proteins.
Briefly discuss serogroups in relation to N. meningitidis.
This refers to the classification of the bacterium based on the antigenic properties of its polysaccharide capsule. The most clinically significant serogroups are A, B, C, W, X, Y and Z.
What are two important clinical manifestations of N. meningitidis infection?
(1) Meningitis
✔ Inflammation of meninges.
✔ Fever, headache, stiff neck, increased PMNs in the spinal fluid, others [nausea, vomiting, photophobia, altered mental status]
(2) Meningococcemia
✔ Bloodstream infection.
✔ Presents with a purpuric rash. Other symptoms: fever, chills, fatigue, muscle aches, rapid breathing.
✔ Complications: septic shock, disseminated intravascular coagulation, multi-organ failure, Waterhouse-Friedrichsen syndrome.
Describe the pathogenesis of Waterhouse-Friderichsen syndrome.
◾ Lipooligosaccharides (LOS) are components of the outer membrane of certain Gram-negative bacteria e.g. Neisseria meningitidis.
◾ They trigger the release of pro-inflammatory cytokines, leading to increased vascular permeability.
◾ The increased permeability allows fluid and immune cells to exude from the blood vessels into the tissues.
◾ Fluid loss and clotting reduce blood flow to vital organs.
◾ In response to decreased perfusion, the body attempts to maintain blood pressure through vasoconstriction.
◾ The reduced blood flow and clotting can lead to ischemia in the adrenal glands, causing adrenal insufficiency.
specimen used in laboratory diagnosis of N. meningitidis
Blood, CSF, disseminated sites
Regarding N. meningitidis, how are blood samples cultured?
✔ The blood is inoculated into a bottle containing a biphasic medium which consists of a liquid phase and a solid phase [Castaneda method]. The culture bottle is incubated at 35 - 37°C in an environment with 5 - 10% carbon dioxide to promote bacterial growth.
✔ After growth on solid phase, organism is subcultured to chocolate blood agar.
colonial morphology of N. meningitidis on chocolate blood agar
Small translucent grey colonies [Image]
What biochemical tests will give positive results when investigating for N. meningitidis?
✔ Oxidase tests
✔ Sugar fermentation tests: ferments glucose and maltose
(a) Name two antibiotics commonly administered to patients with N. meningitidis infection.
(b) State briefly how they work.
Cefotaxime, Ceftriaxone
Both of these drugs are 3rd generation cephalosporin antibiotics. They bind to penicillin-binding proteins on the bacterial cell wall, effectively inhibiting cell wall synthesis thus resulting in bacterial lysis.
N. gonorrheae transmission
◾ sexual transmission
◾ from mother to child during birth
N. gonorrheae virulence factors
(a) Pili and Opa proteins: they facilitate attachment of bacteria to host cells.
(b) Endotoxin: Neisseria gonorrhoeae produces lipooligosaccharide (LOS), which is an endotoxin that can trigger a strong inflammatory response.
(c) IgA protease
(d) Transferrin binding proteins: enable the bacterium acquire iron from host proteins.
