STEPTRACKERMICROBIOLOGY + IMMUNOLOGY | GRAM-NEGATIVE COCCI | HIGH-YIELD REVIEW

Neisseria

Gram-negative, kidney-bean diplococci, oxidase positive — one has a capsule and kills fast through the blood, the other has no capsule and spreads sexually.

FOCUS ON
N meningitidis: polysaccharide capsule, ferments maltose + glucose, lipooligosaccharide (endotoxin) → meningitis + petechial/purpuric rash, Waterhouse-Friderichsen (adrenal hemorrhage). Risk: terminal complement (C5–C9) deficiency, asplenia, eculizumab, dorms. Ceftriaxone; rifampin/ciprofloxacin prophylaxis for contacts; conjugate vaccine. N gonorrhoeae: no capsule, glucose only, pili antigenic variation (no immunity, no vaccine) → urethritis, cervicitis, PID, septic arthritis, neonatal conjunctivitis → ceftriaxone (+ treat chlamydia).
DISEASE
MECHANISM · RISK
CLINICAL PICTURE
DIAGNOSIS · TREATMENT
Meningococcal meningitis
Nasopharyngeal carriage → bloodstream → meninges; capsule + IgA protease
Fever, headache, neck stiffness; teens/young adults, military, dorms
CSF gram ⁻ diplococci in neutrophils · ceftriaxone
Meningococcemia
Lipooligosaccharide → septic shock, DIC
Rapid petechial → purpuric rash, shock
Can kill within hours
Waterhouse-Friderichsen
DIC → bilateral adrenal hemorrhage
Shock with acute adrenal insufficiency
Hydrocortisone + antibiotics
Recurrent Neisseria infection
Deficiency of C5–C9 (membrane attack complex)
Repeated meningococcal or disseminated gonococcal infection
Eculizumab (anti-C5) → vaccinate first
Meningococcal prevention
Close contacts (household, kissing, roommates)
—
Rifampin, ciprofloxacin or ceftriaxone · MenACWY + MenB vaccines
Gonococcal urethritis
Pili and Opa proteins attach; no capsule
Men: purulent discharge, dysuria (often symptomatic)
NAAT · ceftriaxone IM (+ doxycycline if chlamydia not excluded)
Cervicitis & PID
Ascends to tubes
Often asymptomatic → cervical motion tenderness, salpingitis, tubo-ovarian abscess, infertility, ectopic pregnancy
Fitz-Hugh–Curtis: perihepatitis ("violin string" adhesions)
Disseminated gonococcal infection
Bacteremia (menses, pregnancy, complement deficiency)
Triad: tenosynovitis, migratory polyarthralgia, pustular skin lesions — or purulent monoarthritis (knee)
Most common septic arthritis in sexually active young adults
Ophthalmia neonatorum
Passage through infected canal
Hyperpurulent conjunctivitis day 2–5, corneal perforation risk
Erythromycin ointment prophylaxis · ceftriaxone
Pharyngeal & rectal gonorrhea
Oral/anal sex
Often asymptomatic
NAAT of each exposed site

Mechanism — why the MAC matters

Neisseria in bloodThin outer membrane
→
C5b–C9Membrane attack complex
→
Lysis
C5–C9 deficiency or eculizumab
→
No MAC
→
Recurrent Neisseria bacteremia

Meningococcus vs gonococcus

FEATURE
N MENINGITIDIS
N GONORRHOEAE
Capsule
Yes
No
Sugar fermentation
Maltose + glucose
Glucose only
Vaccine
Yes (conjugate, MenB)
None (antigenic variation)
Transmission
Respiratory droplets
Sexual, perinatal
Disease
Meningitis, sepsis
STI, septic arthritis, conjunctivitis

How it's tested

COMMON CONFUSIONNeonatal conjunctivitis by day: chemical (day 1), gonococcal (days 2–5, hyperpurulent), chlamydial (days 5–14, then pneumonia).
THE TRAPA patient starting eculizumab for PNH or aHUS must get meningococcal vaccines first.
YOUR APPROACHGram ⁻ diplococci → site (CSF/blood vs genital/joint) → capsule and sugars → host risk → treatment and contacts.

If you see… think…

College student with fever, neck stiffness, petechial rash → N meningitidis
Shock with bilateral adrenal hemorrhage → Waterhouse-Friderichsen
Third Neisseria infection in a young adult → terminal complement deficiency
Roommate of meningococcal patient → rifampin / ciprofloxacin prophylaxis
Purulent urethral discharge, gram ⁻ diplococci in neutrophils → gonorrhea
Tenosynovitis + pustules + migratory arthralgia → disseminated gonococcal infection
RUQ pain with "violin string" liver adhesions → Fitz-Hugh–Curtis
Purulent conjunctivitis on day 3 of life → gonococcal ophthalmia
No vaccine because of pilus variation → N gonorrhoeae
Ferments maltose → meningococcus