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Bacteroides
ORGANISM:
- Genus: Bacteroides
- Species: fragilis, thetaiotaomicron, melaninogenicus
GENERAL CONCEPTS:
- Bacteroides comprise a major portion of the human normal flora, predominating in the intestinal tract. These organisms are, like other anaerobes, generally opportunistic and can cause a variety of infections throughout the body. The most common infections include pleuropulmonary, intraabdominal and infections of the female urogenital tract. Bacteroides make up about one-third of the total anaerobic isolates obtained from various infections.
- B. fragilis is particularly important because of 1) the frequency of isolation and 2) its resistance to antibiotics.
- Bacteroides produce several exoenzymes including collagenase, neuraminidase, DNAse, heparinase and some proteases. These enzymes may play a role in the pathogenesis of the organism, assisting the bacteria in the invasion of host tissues following an initial trauma.
DISTINCTIVE PROPERTIES:
- Bacteroides are Gram-negative, anaerobic bacilli or cocco-bacilli. Each species is morphologically distinct and most are encapsulated.
- The activity of the Bacteroides LPS endotoxin is reduced compared to other Gram-negative endotoxins because the lipid A moiety has fewer fatty acids and phosphate groups.
- Most B. fragilis strains deconjugate bile acids.
- B. thetaiotaomicron converts lithocholic acid to ethyl ester. This is significant because lithocholic acid may promote the occurrence of tumors; conversion inactivates this carcinogenic potential.
PATHOGENESIS:
- Bacteroides are indigenous normal flora that may be opportunistic under predisposing conditions such as immunosuppression, aminoglycoside therapy, tissue damage, malignancy, etc.
- The production of collagenase seems important in the pathogenesis of B. melaninogenicus while the pathogenesis of B. fragilis is enhanced by production of an anti-phagocytic capsule.
HOST DEFENSES:
- Polymorphonuclear leukocytes provide an important first line of phagocytic defense.
- Anticapsular immunoglobulin plus complement enhance this phagocytosis.
EPIDEMIOLOGY:
- These are infections of endogenous origin.
- The percentage of Bacteroides in the gingival crevice equals about 16-20% of total flora (8-17% in plaque).
- Bacteroides predominate in the feces, reaching densities of 1011/g feces.
DIAGNOSIS:
- Clinical: Clinical diagnosis relies on factors that are general for anaerobic infections including a foul odor of discharge, the localization of the infection, tissue necrosis, production of gas, etc.
- Laboratory: A Gram stain and isolation of the responsible agent can be routine employing appropriate sampling, transport and growth procedures.
CONTROL:
- Sanitary: Generally, avoiding the introduction of bacteria is most important in preventing disease. Proper wound cleansing and surgical procedures can be highly effective.
- Immunological: None are currently in practice.
- Chemotherapeutic: Prophylaxis prior to dental, bowel, gynecological
surgery can prevent infection. Active disease can be treated using carbenicillin, cefoxitin or chloramphenicol.
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