Fusobacterium, Prevotella and Porphyromonas
- Bacterium
Gram-negative
Thin wall with an outer membrane: stains pink.- Exam priority: high
Anaerobes of the mouth and throat behind gum disease, foul-smelling lung abscesses and Lemierre syndrome, a throat infection that clots the neck vein.
Also called: Fusobacterium necrophorum, Fusobacterium nucleatum, Prevotella melaninogenica, Porphyromonas gingivalis, Lemierre syndrome agent
Quick facts
- Type
- Bacterium · Other clinically important bacteria
- Gram / shape
- Gram-negative · Fusobacterium
- Spread
- Endogenous · Aspiration of oral secretions
- Causes
- Lemierre syndrome · Peritonsillar abscess · F
At a glance
- Gram
- Gram-negative
- Shape
- Fusobacterium: long thin rods with tapered ends; Prevotella and Porphyromonas: short pleomorphic rods
- Oxygen
- Obligate anaerobes
- Family
- Fusobacteriaceae, Prevotellaceae, Porphyromonadaceae
Morphology
- Gram-negative anaerobic rods; Fusobacterium nucleatum has pointed, spindle-shaped ends
- Prevotella melaninogenica and Porphyromonas form brown to black pigmented colonies
- Grow only in anaerobic conditions; pus smells foul
Transmission
- Endogenous: they come from the patient's own mouth, throat, gut or genital tract
- Aspiration of oral secretions, dental infection, sore throat or human bites
- Not spread from person to person
Reservoir: Gingival crevices, tonsils and oropharynx; also gut and vagina
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- F. necrophorum: leukotoxin and haemagglutinin; it aggregates platelets and promotes septic thrombophlebitis
- Fusobacterium lipopolysaccharide is a potent endotoxin (shock, disseminated intravascular coagulation)
- P. gingivalis: gingipain proteases that destroy periodontal tissue
- Many Prevotella strains make beta-lactamase, so penicillin alone fails
Diseases it causes
- Lemierre syndrome: pharyngitis, septic thrombophlebitis of the internal jugular vein and septic emboli Deep neck infection and Ludwig angina →
- Peritonsillar abscess and severe pharyngitis in adolescents and young adults Peritonsillar abscess →
- Aspiration pneumonia Aspiration pneumonia and pneumonitis →
- Lung abscess and empyema Lung abscess →
- Periodontitis and necrotizing gingivitis (Vincent angina, with spirochetes) Periodontitis →
- Brain abscess from dental, sinus or ear infection Brain abscess →
- F. nucleatum is found in colorectal tumours; its causal role is still under study Colorectal cancer →
Clinical picture
- Lemierre: a healthy young adult with a sore throat who days later has rigors, tender swelling along the neck and multiple cavitating lung nodules
- Septic emboli may also reach joints, liver and brain
- Aspiration lung abscess in people with alcohol use, seizures or poor dentition; foul-smelling sputum
- Vincent angina: painful ulcerated tonsils or gums with grey pseudomembrane and very bad breath
Diagnosis
- Anaerobic blood cultures; growth can be slow
- Contrast-enhanced CT of the neck shows internal jugular vein thrombosis; chest CT shows septic emboli
- Pus aspirated and sent in anaerobic transport; Gram stain shows mixed Gram-negative rods
- PCR detects F. necrophorum when cultures fail
Treatment
Drainage of pus plus antibiotics active against anaerobes: metronidazole (combined with a beta-lactam for streptococci), a beta-lactam/beta-lactamase inhibitor (ampicillin-sulbactam, amoxicillin-clavulanic acid, piperacillin-tazobactam), a carbapenem, or clindamycin for oral infections. Penicillin alone is unreliable because of beta-lactamase; anticoagulation in Lemierre syndrome is debated.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
- Metronidazole
- Ampicillin + sulbactam
- Amoxicillin + clavulanic acid
- Clindamycin
- Piperacillin + tazobactam
- Meropenem
Prevention
- Oral hygiene and regular dental care
- Aspiration precautions: upright position and swallowing assessment in at-risk patients
- Early review of a sore throat that worsens with rigors or neck pain
Test yourself
Think of the answer, then tap the question to see it.
Which organism causes most cases of Lemierre syndrome?
Fusobacterium necrophorum, an anaerobic Gram-negative rod.
Which vein is involved in Lemierre syndrome?
The internal jugular vein, with septic thrombophlebitis.
Why may penicillin alone fail in oral anaerobic infections?
Many Prevotella and some Fusobacterium strains produce beta-lactamase.
Which anaerobes form black-pigmented colonies?
Prevotella melaninogenica and Porphyromonas species.
Which imaging test confirms internal jugular vein thrombosis in Lemierre syndrome?
Contrast-enhanced CT of the neck (ultrasound is less sensitive).
Connections
← Back to the group: Other clinically important bacteria
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Lemierre's Syndrome in the 21st Century: A Literature Review (Cureus, 2023); Mixed Anaerobic Infections - Infectious Disease - MSD Manual Professional Edition (MSD Manual Professional Edition, 2025).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.