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Anaerobic Bacteria
Anaerobiosis
Anaerobic bacteria will not grow in the presence of oxygen.
Possible mechanisms:
1) Lack of cytochrome systems for the metabolism of
O2.
2) Short of superoxide dismutase.
3) Short of catalase.
4) other unknown mechanisms.
Ability of anaerobes to tolerate oxygen or grow in its
presence varies from species to species. Most anaerobic
clinical isolates are moderately obligate anaerobes, and have
small amount of both catalase and superoxide dismutase.
Methods for excluding oxygen
1. Fluid media containing
fresh animal tissue or 0.1%
agar containing a reducing
agent, thioglycollate.
2. Anaerobic jar
3. Anaerobic glove chamber
Non-sporeforming anaerobes
Bacteroides, Fusobacterium, Porphyromonas, Prevotella,
Veillonella, Actinomyces, Propionibacterium, Peptostreptococcus
1. Non-sporeforming anaerobes
constitute the predominant part
of normal indigenous flora in
human body.
2. Diseases caused by them
are usually not transmissible
and are almost autoinfection.
The result is usually tissue
necrosis and abscess formation.
3. Types of infections are
related to the normal
endogenous location of the
bacteria (Table 42-1).
4. Most infections caused by
them are mixed, containing 5-6
species or more, including both
anaerobes and facultative
anaerobes (synergism).
5. In most cases, treatment
requires drainage of the
purulent material and
appropriate chemotherapy (e.g.,
metronidazole, clindamycin,
etc.)
Bacteroides fragilis
Pleomorphic in size and shape; capsulated.
Aerotolerant; growth is stimulated in 20% bile.
Constitutes less than 10% of Bacteroides species in the
normal colon, however, is the most common isolate of
anaerobes from infections (intra-abdominal, gynecologic,
and skin and soft tissue infections; bacteremia.)
Major virulence factor: capsular polysaccharides, which
may cause abscess formation when injected into the rat
abdomen.
Its LPS lacks endotoxin activity. The clinical signs of
sepsis (fever & shock) could be due to other components.
Resistant to penicillin.
B. fragilis