Prevotella / Fusobacterium spp.
Anaerobic Gram-negative bacilli
Identification & Growth
Identification
- Prevotella: black pigment on laked blood agar, brick-red fluorescence under UV light
- Fusobacterium: fusiform bacilli with tapered ends
Growth Conditions
- Brucella/laked blood agar with hemin and vitamin K, anaerobic incubation, 48–72 h
Clinical Significance
- Periodontal abscess, aspiration pneumonia, chronic sinusitis
- Fusobacterium necrophorum: Lemierre's syndrome
Intrinsic Resistance
- Resistant to aminoglycosides, aztreonam and trimethoprim-sulfamethoxazole
Bench Alerts
- Increasing beta-lactamase production: report amoxicillin-clavulanate or metronidazole
- Collection in an air-free syringe or anaerobic transport medium is essential
Clinical Notes
Clinical presentations
- Odontogenic infections, peritonsillar abscess, chronic sinusitis and aspiration lung abscess.
- Fusobacterium necrophorum causes Lemierre syndrome: pharyngitis followed by internal jugular thrombophlebitis and septic pulmonary emboli.
- Prevotella takes part in pelvic infections, intra-abdominal abscesses and diabetic foot infection, almost always in mixed culture.
Specimens and collection
- Abscess aspirate or tissue fragment in anaerobic transport medium; a superficial swab is inadequate.
- Transport within 2 h and avoid refrigeration, which reduces recovery of strict anaerobes.
- An anaerobic blood-culture bottle is essential when Lemierre syndrome is suspected.
Epidemiology and at-risk populations
- They are part of the oral, gastrointestinal and female genital microbiota, becoming pathogenic after barrier breakdown.
- Lemierre syndrome typically affects previously healthy adolescents and young adults.
- Aspiration, periodontal disease, abdominal surgery and immunosuppression are the main predisposing factors.
Resistance and therapeutic implications
- Beta-lactamase production is frequent in Prevotella: penicillin alone is unreliable; use a beta-lactamase inhibitor combination.
- Metronidazole, carbapenems and beta-lactam/inhibitor combinations retain good activity; clindamycin resistance is increasing.
- Anaerobes are intrinsically resistant to aminoglycosides and aztreonam — never report these classes as susceptible.
Bench and reporting notes
- Pigmented Prevotella produce dark-brown colonies and brick-red fluorescence under UV on laked blood agar.
- Fusobacterium appears on Gram stain as a fusiform rod with tapered ends — a suggestive finding already on microscopy.
- Anaerobe susceptibility testing is reserved for severe infection, treatment failure or surveillance; state the method (MIC) in the report.
Sources
- EUCAST — Clinical breakpoints (v16.1)
- EUCAST — Expert rules and expected resistant phenotypes
- UKHSA — Standards for Microbiology Investigations (SMI)
Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.
FAQ: Frequently Asked Questions
How to identify Prevotella / Fusobacterium spp. in the lab?
Prevotella / Fusobacterium spp. is identified through prevotella: black pigment on laked blood agar, brick-red fluorescence under uv light, fusobacterium: fusiform bacilli with tapered ends.
What are the intrinsic resistances of Prevotella / Fusobacterium spp.?
This organism is naturally resistant to resistant to aminoglycosides, aztreonam and trimethoprim-sulfamethoxazole. These drugs should not be reported as susceptible.
Where is Prevotella / Fusobacterium spp. commonly found?
It is typically associated with periodontal abscess, aspiration pneumonia, chronic sinusitis, fusobacterium necrophorum: lemierre's syndrome.
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