Lecture 5: Neisseria (Gram-Negative Cocci) Flashcards
What are the key features of Neisseria spp.?
Gram-negative diplococci, oxidase-positive, catalase-positive, fastidious (requires CO₂), aerobic/capnophilic, pili for adhesion.
How can N. meningitidis and N. gonorrhoeae be differentiated?
Meningococcus: Capsulated (serogroups A/B/C/Y/W135), variable catalase, nasopharyngeal carriage.
Gonococcus: Non-capsulated, strong catalase, genital tract infection.
Name 4 key virulence factors of N. meningitidis.
Capsule: Prevents phagocytosis (serogroups A/B/C/Y/W135).
Pili (PilE/PilC): Mediate adhesion to epithelial cells.
LOS (Lipo-oligosaccharide): Endotoxin released in blebs → septic shock.
Porins (PorA/PorB): Inhibit phagosome maturation.
Describe the steps of N. meningitidis infection.
Adhesion: Pili bind to nasopharyngeal epithelium.
Invasion: Opa proteins trigger cytoskeletal rearrangements → transcytosis.
Dissemination: Enters bloodstream (bacteremia) → meningitis/septicemia.
How does N. meningitidis evade complement?
Binds Factor H (via PorB/sialic acid) → inactivates C3b.
Binds C4bp (via pili) → inactivates C4b.
Capsule limits complement deposition.
What are the symptoms of meningococcemia?
Fever, hemorrhagic rash (80%), septic shock, DIC, multi-organ failure. Rapid progression (<24 hrs).
How is N. meningitidis diagnosed?
CSF Gram stain: Gram-negative diplococci.
Culture: Chocolate agar (CO₂), oxidase-positive.
NAAT: Detects bacterial DNA in blood/CSF.
Compare the MenB and MenACWY vaccines.
MenB (Bexsero): Targets factor H-binding protein (not capsule).
MenACWY: Capsular polysaccharide conjugated to protein (serogroups A/C/Y/W135).
What is the management of meningococcal disease?
Antibiotics: Ceftriaxone/penicillin (IV).
Prophylaxis: Rifampicin/ciprofloxacin for close contacts.
Who is at highest risk for N. meningitidis infection?
Infants (<5 yrs), teenagers (dorms), immunocompromised, complement-deficient individuals.
