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Bacteroides fragilis

  • General information


    • Bacteroides fragilis group, are the most frequently encountered anaerobes in clinical specimens.

      They tend to be more virulent and drug resistant than most other anaerobes.

      Therefore it is important to identify members of the B. fragilis group
      Of these especially B. fragilis, B. thetaiotaomicron, and B. ovatus are highly relevant in human infections.

      Taxonomy
      Family: Bacteroidaceae

      Natural habitats
      They inhabit the mucosal surfaces of the oral cavity, gastrointestinal tract and the gut of animals and human.

      Clinical significance
      They are involved in a variety of infections associated with considerable morbidity and mortality.

      Anaerobic bacteria can occasionally spread to the adjacent tissues and the bloodstream with serious consequences.
      In cases when gram negatives anaerobes gain entrance to the bloodstream and trigger a systemic inflammatory response, this may result in a sepsis or infective endocarditis with a fatal outcome.

  • Gram stain

    • Light colored, short, Gram negative rods,

      0.5-0.8 x 1.5-4.5 µm,

      with rounded ends, lying alone or in pairs.

      B. fragilis often resemble safety pins

      Liquid medium:
      cells tend to be pleomorphic often with vacuoles

  • Culture characteristics

    • Obligate anaerobic

      BBAØ: t
      he colonies are gray, circular, convex and entire

      BBEØ: growth with gray or black colonies > 1 mm and causing browning of the medium as a result of esculin hydrolysis

      Except for B. vulgatus (pale colonies)

      Fluorescence under long-wave UV light (Woods lamp)
      Negative

  • Characteristics

  • References

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