Bacteroides and Prevotella are gram negative rods, non- spore forming, encapsulated, anaerobic and non-motile bacteria.
Route of entry
Part of normal flora, colonize human colon and vagina.
• Infections are endogenous, following a break in the mucosal surface, organism causes infections.
• Local abscesses are formed at the site of mucosal breaks.
• Metastatic abscesses form by hematogenous spread to other organs.
• Lung abscesses occur by aspiration of oral flora.
• Facultative anaerobic conditions are required.
• Endotoxin (lipopolysaccharide) produces sepsis and septic shock
• Enzymes causes tissue damage:
• Polysaccharide capsule is antiphagocytic
• B- lactamase
• Chronic disease
• Local tissue necrosis
• Impaired blood supply
• Growth of facultative anaerobes at the site
• Intra-abdominal infections
• Pelvic abscesses
• Necrotizing bacteremia
Bacillus Fragilis causes disease below the diaphragm and B. melaninogenicus causes disease above the diaphragm.
• Inflected tissue
Important features observed under microscope include:
• Gram- negative rods
• Non- spore forming
• Non- Motile
Blood agar plus vancomycin
Grey, glistening colonies are formed which are non- haemolytic
• Sugar fermentation
• Organic acid production detected by gas chromatography