• Gram negative anaerobic rod
• Shape: Pleuromorphic
• Size: (0.5-1.5)µm wide and (2-6)µm long
• Non motile except B. polypragmatus, B. xylanolyticus
• Non capsulated except fragilis
• Non spore forming
• Habitat: Norma flora of gastrointestinal tract, mouth, skin, nasopharyns, Upper respiratory tract, vagina
• Opportunistic human pathogen

Classification of Bacteroides

• on the basis of medical importance bacteriodes is classified into two group

1. Bacteroides fragilis group:

• Examples:
  • B.fragilis
  • B. distasonis
  • B. ovatus,
  • B. thetaiotaomicron
  • B. vulgatus
  • B. idgatus
  • B. uniformis
  • B. tiariabilisleggerthii
  • B. splanchnicus
• these are commensals of GI tract

2. Bacteroides melaninogenicus group

• Examples:
  • B. melaninogenicus sub spp intermedius
  • B. ruminicola
• Now the name has changed to Prevotella melaningenica
• these are Norma flora of URT, GIT, vagina

Pathogenesis:

1. Mode of transmission:

• Displacement of their normal habitat

2. Virulence factors of Bacteroides

• i) Capsule:- Helps in attachment, and resist phagocytosis and complement mediated lysis.
• ii) Fimbriae: helps in attachment
• iii) Endotoxin (LPS):- stimulates leucocytes
• iv) Short chain Fatty acids (succinic acid):- resist phagocytosis and intracellular killing
• v) Enzymes- protect from Oxygen toxicity
  • Catalase and Superoxide dismutase: These enzymes inactivates H2O2 and release super oxide free radicals there by protect anaerobes when exposed to oxygen
  • Protease
  • Collagenase
  • Phospholipase
  • Neuraminidase
  • Heparinase
  • Haemolysin
  • Fibrinolysin
  • Gluconidase

Clinical manifestation of Bacteroides:

• Genitourinary tract infection
• Appendicitis
• Bacteriaemia
• Endocarditis, pericarditis, vascular graft infection
• Meningitis
• Septic artheritis
• Bed sore
• Inflammation of viscent angina ( throat)
• Skin and soft tissue infection
• Upper respiratory infection

Laboratory diagnosis of Bacteroides

Samples: pus, exudates, biopsy

1. Microscopy:

• gram negative, non motile, non sporing pleuromorphic rod

2. Culture:

i) Blood Agar (BA):

• Kanamycin or neomycin Blood agar selective for Anaerobes
• Inculates anaerobically at 37C for 48 hours
• fragilis Form non haemolytic grey colony of 1-3 mm diameter
• melanogenicus form black brown haemolytic colony in 3-5 days

ii) Bactrroides Bile Esculin Agar (BBE):

• hydrolyses esculin,
• colony surrounded by dark zone

3. Biochemical tests for fragilis

• i) Esculin hydrolyses: positive (+)
• ii) Indole: negative (-)
• iii) Urease: Negative (-)
• iv) Catalase: Positive (+)
• v) Oxidase : variable (+/-)
• vi) Fermentative: glucose +, lactose +, maltose +, sucose + rhamnose -, Arabinose -, salicin -, trehalose –
• vii) Bile resistant: grow in 20% bile
• viii) Thioglycolate with bile: Positive (+)
• ix) Beta lactamase production: fragilis is resistant to penicillin

4. Serology

5. PCR

Treatment of Bacteroides:

1. Metronidazole: drug of choice
2. Cephalosporin
3. Chloramphenicol

Bacteroides: Classification, virulence factors and biochemical tests

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