Bacteroides | Anatomy2Medicine
Bacteroides Infections

Bacteroides

 

  • Anaerobic gram-negative rods
      • most common organ-sms in the oral cavity (particularly the gingiva), female genital tract, and lower GI tract,
      • hey outnumber Escherichia coli 1,000:1.
      • recovered in about 10 percent of bacteremias
      • constitute the majority of organisms associated with anaerobic abscesses.
      • A localized abscess is the most common lesion
  • various facultative organisms help lower the pO2, thus providing the anaerobic environment required by the coinfecting gram-negative rods (MCQ)
  • Bacteroides
      • predominant anaerobes found in the human colon.
      • It is part of the normal flora
      • only cause disease when they gain access to tissues or the blood during bowel penetration (for example, during surgery or trauma).
      • They are, however, the most common cause of serious infections by anaerobic organisms.
      • slender rods or coccobacilli.
      • Their polysaccharide capsule is an important virulence factor, conveying resistance to phagocytosis. (MCQ)
      • Source of infection is endogenous (it is not transmitted from per- son to person). (MCQ)
  • Laboratory identification:
        • Exudates are often copious and noticeably foul smelling
        • A Gram stain of such exudates shows numerous faint, slender, gram-negative rods, usually in mixed flora (MCQ)
        • cultured on blood agar under anaerobic conditions(MCQ)
        • Gas chromatography can be used to identify the characteristic short-chain fatty acids produced by the organism(MCQ)
  • biochemical tests can determine its sugar fermentation pattern.
  • B. melaninogenica
        • Is black or brown colour of the colonies. (MCQ)
        • The colour is not due to the melanin pigment as was once thought but to a hemin derivative. (MCQ)
        • It has been isolated from various infections including lung or liver abscess, mastoiditis, intestinal lesions and lesions of the mouth and gums.
        • Cultures of B. melaninogenica and even dressings from wounds infected with the bacillus give a characteristic red fluorescence when exposed to ultraviolet light.
    • Treatment and prevention:
      • Metronidazole is the antibiotic of choice for B. fragilis infections. (MCQ)
      • Aminoglycosides are, of course, ineffective against anaerobes (MCQ)
      • Surgical drainage of any abscess is essential to ensure penetration of drugs.
      • To prevent Bacteroides contamination of a surgical wound, a perioperative antibiotic, such as cefoxitin, can be administered (MCQ)