Bacteroides fragilis

Background:

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Anaerobic Gram-Negative Bacilli
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>Bacteroides fragilis (most important clinically)

    [Other Bacteroides species – less common clinically: (B. acidifaciens, B. gracilis,
         B. oris, B. ovatus, B. pyogenes , B. stercoris, B. vulgatus)]
>Bacteroides melaninogenicus (reclassified and split into Prevotella melaninogenica
     and Prevotella intermedia.)
>Fusobacterium necrophorum
>Porphyromonas gingivalis

Bacteroides fragilis:

Gram-negative bacillus bacterium species, and an obligate anaerobe of the gut.
B. fragilis group is the most commonly isolated Bacteroidaceae in anaerobic infections (especially those that originate from the gastrointestinal flora).
B. fragilis is the most prevalent organism in the B. fragilis group, accounting for 41% to 78% of the isolates of the group.
These organisms are resistant to penicillin by virtue of production of beta-lactamase, and by other unknown factors.
B. fragilis is involved in 90% of anaerobic peritoneal infections.

Therapy:

Important considerations: The choice of an agent should be based on local antimicrobial sensitivities, site of infection, cost, and comorbid conditions. Generally, the most common agents/regimens are listed first.

Mild to moderate infections:
- Metronidazole 500mg IV/PO every 6 hours
- Augmentin 875/125 mg orally twice daily OR Ampicillin-sulbactam (Unasyn®) 1.5 – 3.0 grams IV q6h
- Cefoxitin 1-2 gm IV q6h (increasing resistance)
- Moxifloxacin 400mg orally/IV qd (increasing resistance)
- Tigecycline 100 mg IV x 1, then 50 mg q12h
- Combination examples: [ceftriaxone, cefotaxime, ciprofloxacin (IV/Oral), or levofloxacin (IV/Oral)] PLUS Metronidazole 500mg IV/PO every 6 hours
Severe infections:
- Piperacillin-tazobactam (Zosyn ®) 3.375 to 4.5 grams IV q6h
- Imipenem 500mg IV every 6 hours [Range: 250-1000 mg q6-8h]
- Meropenem 0.5 – 1 gram IV q8h
- Doripenem 500 mg IV q8h
- Combination examples: [Cefepime, ceftazidime, ciprofloxacin (IV), or levofloxacin (IV) ] PLUS Metronidazole 500mg IV every 6 hours

Disclaimer

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