Anaerobes (gram positive and negative):

Empiric drug regimens listed for the various bacterial strains are for ADULT patients with normal renal function. Review the relevant package insert for additional prescribing information.

Anaerobic Gram-Negative Bacilli
>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

Anaerobic Gram-Negative cocci
-Veillonella parvula

Anaerobic Gram-positive cocci
Peptostreptococcus species

Anaerobic Gram-positive bacilli
1] Gram-positive spore-forming:
>Clostridium species

2]  Gram-positive nonspore-forming bacilli:
>Bi?dobacterium species



  • Anaerobic bacteria do not grow on solid media in room air (0.04% carbon dioxide and 21% oxygen).
  • Facultative anaerobic bacteria can grow in the presence as well as in the absence of air.
  • Microaerophilic bacteria do not grow at all aerobically or grow poorly, but grow better under 10% carbon dioxide or anaerobically.
  • Anaerobic bacteria can be divided into strict anaerobes that can not grow in the presence of more than 0.5% oxygen and moderate anaerobic bacteria that are able of growing between 2 to 8% oxygen.
  • Anaerobic bacteria usually do not possess catalase, but some can generate superoxide dismutase which protects them from oxygen.
  • The clinically important anaerobes in decreasing frequency are:
    • 1. Six genera of Gram-negative rods (Bacteroides, Prevotella, Porphyromonas, Fusobacterium, Bilophila and Sutterella spp.);
    • 2. Gram-positive cocci (primarily Peptostreptococcus spp.);
    • 3. Gram-positive spore-forming (Clostridium spp.) and nonspore-forming bacilli (Actinomyces, Propionibacterium, Eubacterium, Lactobacillus and Bi?dobacterium spp.); and
    • 4. Gram-negative cocci (mainly Veillonella spp.) .
  • Because of their fastidious nature, anaerobes are hard to isolate and are often not recovered from infected sites.


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