Anaerobes

Anaerobes (gram positive and negative):

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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

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Anaerobic Gram-Negative cocci
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Veillonella
-Veillonella parvula

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Anaerobic Gram-positive cocci
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Peptostreptococcus species

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

2]  Gram-positive nonspore-forming bacilli:
>Actinomyces
>Bifidobacterium species
>Eubacterium
>Lactobacillus
>Propionibacterium

Comments:

• 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.