Neisseria meningitidis vs Neisseria gonorrhoeae
How to tell Neisseria meningitidis and Neisseria gonorrhoeae apart when a board question makes them look alike.
Meningitidis ferments glucose and maltose and causes meningitis; gonorrhoeae ferments glucose only and causes STI disease.
Side by side
Meningitis or meningococcemia with petechiae, septic shock, and glucose-plus-maltose fermentation.
Urethritis/cervicitis, PID, neonatal conjunctivitis, or disseminated arthritis-dermatitis with glucose-only fermentation.
Encapsulated meningococcus spreads via respiratory droplets and causes endotoxin-mediated vascular injury.
Gonococcus attaches to mucosal epithelium with pili and varies surface antigens to evade immunity.
CSF or blood intracellular gram-negative diplococci with maltose fermentation points meningitidis.
Urethral/cervical intracellular gram-negative diplococci with glucose-only fermentation points gonorrhoeae.
The trap
Both are gram-negative diplococci that grow on Thayer-Martin agar, so the gram stain alone is not enough. The deciding clues are site of infection, sugar fermentation, and capsule. N. meningitidis ferments BOTH glucose and Maltose (mnemonic: Meningitidis Maltose), has a polysaccharide capsule (vaccine-preventable serogroups A, C, W, Y plus serogroup B), causes meningitis and Waterhouse-Friderichsen syndrome with bilateral adrenal hemorrhage; classic in college dorms, military barracks, hajj pilgrims. Close contacts need post-exposure prophylaxis with rifampin, ciprofloxacin, or ceftriaxone. N. gonorrhoeae ferments Glucose only (mnemonic: Gonorrhea Glucose), has NO polysaccharide capsule (no vaccine, just IgA1 protease), causes urethritis, cervicitis, PID, disseminated gonococcal infection (migratory polyarthralgia, tenosynovitis, pustular skin lesions), and ophthalmia neonatorum (prevent with erythromycin eye drops at birth).
Watch it explained
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For Neisseria, ask: meninges/blood or genital mucosa, then glucose-only versus glucose-plus-maltose.
Try a free question
CoreA college student develops fever, neck stiffness, petechial rash, and septic shock. Gram stain shows intracellular gram-negative diplococci. Which organism is most likely?
Show answer and explanation
Answer: A. Neisseria meningitidis. N meningitidis causes meningitis and meningococcemia with petechiae; it ferments glucose and maltose.
Why the other choices are tempting
- B. N gonorrhoeae causes urethritis/cervicitis, PID, septic arthritis, and neonatal conjunctivitis; it ferments glucose only.
- C. Hib is a gram-negative coccobacillus, not diplococcus.
- D. S pneumoniae is gram-positive lancet-shaped diplococcus.
- E. Listeria is a gram-positive rod.
Flashcards
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What is the fastest separator for Neisseria meningitidis vs Neisseria gonorrhoeae?
Meningitidis ferments glucose and maltose and causes meningitis; gonorrhoeae ferments glucose only and causes STI disease.
What clue should make you choose Neisseria meningitidis?
Meningitis or meningococcemia with petechiae, septic shock, and glucose-plus-maltose fermentation.
Quick answers
What is the fastest way to tell Neisseria meningitidis from Neisseria gonorrhoeae?
Meningitidis ferments glucose and maltose and causes meningitis; gonorrhoeae ferments glucose only and causes STI disease.
What is the key clue for Neisseria meningitidis?
Meningitis or meningococcemia with petechiae, septic shock, and glucose-plus-maltose fermentation.
What is the key clue for Neisseria gonorrhoeae?
Urethritis/cervicitis, PID, neonatal conjunctivitis, or disseminated arthritis-dermatitis with glucose-only fermentation.
What is the common trap with Neisseria meningitidis vs Neisseria gonorrhoeae?
Both are gram-negative diplococci that grow on Thayer-Martin agar, so the gram stain alone is not enough. The deciding clues are site of infection, sugar fermentation, and capsule. N. meningitidis ferments BOTH glucose and Maltose (mnemonic: Meningitidis Maltose), has a polysaccharide capsule (vaccine-preventable serogroups A, C, W, Y plus serogroup B), causes meningitis and Waterhouse-Friderichsen syndrome with bilateral adrenal hemorrhage; classic in college dorms, military barracks, hajj pilgrims. Close contacts need post-exposure prophylaxis with rifampin, ciprofloxacin, or ceftriaxone. N. gonorrhoeae ferments Glucose only (mnemonic: Gonorrhea Glucose), has NO polysaccharide capsule (no vaccine, just IgA1 protease), causes urethritis, cervicitis, PID, disseminated gonococcal infection (migratory polyarthralgia, tenosynovitis, pustular skin lesions), and ophthalmia neonatorum (prevent with erythromycin eye drops at birth).