Pathogenic anaerobesPathogenic anaerobes

Anaerobic bacteria are widely distributed in nature in oxygen-free habitats.

Many members of the indigenous human flora are anaerobic bacteria, including

SpirocheteGram-positive cocci and bacilli Gram-negative cocci and bacilli

Normal places for anaerobics:Normal places for anaerobics:Colon: contains large populations of anaerobic bacteria,

exceeding 1011 organisms/gr of colon content.

Gingival crevicesGingival crevices

Tonsillar cryptsTonsillar crypts

Nasal foldsNasal folds

Hair folliclesHair follicles

UrethraUrethra

VaginaVagina

Tooth surfacesTooth surfaces

Ecology of anaerobic Ecology of anaerobic in the bodyin 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.

Anaerobes multiply well in dead tissue.

Multiplication of aerobic or facultative organisms in association with anaerobes in infected tissue also diminishes oxygen concentration.

Ecology of anaerobic Ecology of anaerobic in the bodyin the body

The types of anaerobic infectionsThe types of anaerobic infections

1. Intra-abdominal infectionsIntra-abdominal infections

Abscesses

Postoperative wound infections

Generalized peritonitis

Occur as a consequence of

bowel perforation during surgery or

injury.

2. Pulmonary infectionsPulmonary 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 infectionsPelvic infections

Due to gynecologic surgery or in association with malignancy of pelvic organs.

4. Brain abscessesBrain abscesses

(The infecting organisms usually originate in the upper respiratory tract.)

Meningitis

Brain abscesses

5. Skin and soft tissue infectionsSkin and soft tissue infections

Combination of anaerobes, aerobes, and facultative organisms often act synergistically

6. Oral and dental infectionsOral 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 endocarditisBacteremia 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 bacteriaThe list of anaerobic bacteria

Bacilli Gram positive: ClostridiaGram Negative: Bacteroides, porphyromonas,

Fusobacterium

CocciGram positive: PeptostreptococcusGram negative: Veillonella, Acidominococcus

MegosphoraSpirochetes: includes both aerobic and anaerobic species

BacteroidesBacteroides

Important properties: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 EpidemiologyPathogenesis 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 factorsVirulence factorsof B. fragilis

The polysaccharide capsule No exotoxin have been found.

Clinical findingClinical findingThe B. fragilis B. fragilis is frequently associated with:

- Peritonitis

- Localized abscesses

- Pelvic abscesses

- Bacteremia

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.

Laboratory diagnosisLaboratory diagnosis

Treatmentfor 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

PreventionPrevention

No vaccine

Per-operative administration of a cephalosporins (frequently cefoxitin) for abdominal or pelvic surgery.