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Pathogenic anaerobes
Anaerobic bacteria are widely distributed in
nature in oxygen-free habitats.
Many members of the indigenous human flora
are anaerobic bacteria, including
Spirochete
Gram-positive cocci and bacilli
Gram-negative cocci and bacilli
Normal places for anaerobics:
Colon: contains large populations of anaerobic bacteria,
exceeding 1011 organisms/gr of colon content.
Gingival crevices
Tonsillar crypts
Nasal folds
Hair follicles
Urethra
Vagina
Tooth surfaces
Ecology of anaerobic
in the body
Anaerobic indigenous flora components are
potentially pathogenic if displaced from their normal
habitat.
Proliferation of anaerobic bacteria in tissue depends
on the absence of oxygen.
Oxygen is excluded from the tissue when the local
blood supply is impaired by trauma, obstruction, or
surgical manipulation.
Ecology of anaerobic
in the body
Anaerobes multiply well in dead tissue.
Multiplication of aerobic or facultative organisms in
association with anaerobes in infected tissue also
diminishes oxygen concentration.
The types of anaerobic infections
1. Intra-abdominal infections
Abscesses
Postoperative wound infections
Generalized peritonitis
Occur as a
consequence of
bowel perforation
during surgery or
injury.
2. Pulmonary infections
Anaerobic lung infections may originate in the bronchi
or the blood.
Aspirations from the upper respiratory tract are
responsible for initiating infection in the bronchi.
3. Pelvic infections
Due to gynecologic surgery or in association with
malignancy of pelvic organs.
4. Brain abscesses
(The infecting organisms usually originate in the
upper respiratory tract.)
Meningitis
Brain abscesses
5. Skin and soft tissue infections
Combination of anaerobes, aerobes, and facultative
organisms often act synergistically
6. Oral and dental infections
These local infections frequently extend to the face and
neck and sometimes to other areas of the body such
as the brain.
7. Bacteremia and endocarditis
Endocarditis, an inflammation of the endothelial
lining of the heart cavities is occasionally caused by
anaerobic bacteria, especially anaerobic streptococci.
The list of anaerobic bacteria
Bacilli
 Gram positive: Clostridia
 Gram Negative: Bacteroides, porphyromonas,
Fusobacterium
Cocci
 Gram positive: Peptostreptococcus
 Gram negative: Veillonella, Acidominococcus
Megosphora
 Spirochetes: includes both aerobic and anaerobic
species
Bacteroides
Important properties:
 Anaerobic, non-spore-forming, Gram negative rods.
 Of 22 species, 3 are human pathogens:
1. Bacteroides fragilis
2. Bacteroides melaninogenicus
3. Bacteroides corrodens
Members of the B. fragilis group are the
predominant organisms in the human colon,
numbering approximately 1011/g of feces, and are
found in the vagina of approximately 60% of women.
B. melaninogenicus and B. corrodens are normal oral
flora but found in lung abscesses.
Pathogenesis and Epidemiology
Local mucosal abscesses due to a break in a mucosal
surface
Metastatic abscesses by hematogenous spread to
distant organs
Lung abscesses by aspiration of oral flora.
Virulence factors
of B. fragilis
 The polysaccharide capsule
 No exotoxin have been found.
Clinical finding
The B. fragilis is frequently associated with:
- Peritonitis
- Localized abscesses
- Pelvic abscesses
- Bacteremia
Laboratory diagnosis
Culture on blood agar containing kanamycin and
vancomycin to inhibit unwanted organisms.
Identification by biochemical reactions (eg. Sugar
fermentations) and by production of certain organic
acids (eg. Formic, acetic, and propionic acids) which
are detected by gas chromatography.
Treatment
for members of B. fragilis
Clindamycin is the drug of choice
Resistant to penicillin, first generation of
cephalosporins and aminoglycosides.
Aminoglycosides treat the facultative gram-negative
rods in mixed infections.
Seurgical drainage of abscesses
Treatment for
B. melaninogenicus
Highly susceptible to penicillin G
Seurgical drainage of abscesses
Prevention
No vaccine
Per-operative administration of a cephalosporins
(frequently cefoxitin) for abdominal or pelvic
surgery.