Bacteroides fragilis

Bacteroides fragilis

Background:
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Anaerobic Gram-Negative Bacilli
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>Bacteroides fragilis (most important clinically)Led
    [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.

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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.

  1. 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
  2. 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

Specific Bacterial Pathogens

  1. Achromobacter xylosoxidans
  2. Acinetobacter baumannii
  3. Actinomyces
  4. Actinomyces israelii
  5. Aeromonas species
  6. Bacillus species
  7. Bacteroides fragilis
  8. Bacteroides melaninogenicus
  9. Bartonella species
  10. Bordetella pertussis
  11. Borrelia species
  12. Brucella species
  13. Burkholderia species
  14. Campylobacter
  15. Capnocytophaga species
  16. Chlamydophila pneumoniae
  17. Chlamydophila psittaci
  18. Citrobacter species
  19. Clostridium species
  20. Corynebacterium species
  21. Coxiella burnetii
  22. Ehrlichia species
  23. Eikenella corrodens
  24. Enterobacter species
  25. Enterococcus faecalis
  26. Enterococcus faecium
  27. Escherichia coli
  28. Francisella tularensis
  29. Fusobacterium necrophorum
  30. Gardnerella vaginalis
  31. Haemophilus species
  32. Helicobacter Pylori
  33. Klebsiella species
  34. Lactobacillus species
  35. Legionella species
  36. Leptospira species
  37. Listeria monocytogenes
  38. Moraxella catarrhalis
  39. Morganella species
  40. Mycoplasma pneumonia
  41. Neisseria species
  42. Nocardia species
  43. Pasteurella multocida
  44. Peptostreptococcus species
  45. Porphyromonas gingivalis
  46. Propionibacterium acnes
  47. Proteus species
  48. Providencia species
  49. Pseudomonas aeruginosa
  50. Salmonella species
  51. Serratia marcescens
  52. Shigella species
  53. Staph epidermidis
  54. Staph hominis
  55. Staph. haemolyticus
  56. Staphylococcus aureus
  57. Staphylococcus saprophyticus
  58. Stenotrophomonas maltophilia
  59. Streptococcus agalactiae
  60. Streptococcus anginosus group
  61. Streptococcus pneumoniae
  62. Streptococcus pyogenes (Groups A, B, C, G, F)
  63. Treponema pallidum
  64. Vibrio species
Bacteroides fragilis