This document summarizes several genera of anaerobic bacteria commonly found in the human gastrointestinal tract. It describes their role in metabolism and protection against pathogens. Key points include: - Bacteroides, Prevotella, and Veillonella are commensal bacteria that assist in food breakdown and nutrient production. Fusobacterium and Porphyromonas can cause infections. - Virulence factors include capsules, pili, enzymes. Diagnosis involves gram stain and culture with identification by biochemical tests. - Treatment involves metronidazole, clindamycin and surgical drainage of abscesses. Prevention focuses on perioperative antibiotics for surgery.

1. Bacteroides
Bacteroides, Fusobacterium,
Porphyromonas, Prevotella, Veillonella
• Anaerobic, gram-negative rods predominant genus in the
human intestine.
• Important in numerous metabolic activities and may provide
some level of protection from invasive pathogens.
• Assist in breaking down food and producing valuable
nutrients and energy that the body need.
• Responsible for many types of infections and abscesses.

2. Virulence factors
• Polysaccharide capsule
• Pili and fimbriae
• Lipopolysaccharide
• Enzymes: hyaluronidase, hemolysin, peroxidase, collagenase, protease,
heparinase, and neuraminidase.
Lab Diagnosis
• Gram-stained smear plus anaerobic
culture
• Identification based on biochemical
reactions and gas chromatography
• Serological tests not useful
On K-V Agar with 5% Sheep Blood
Bacteroides Bile Esculin (BBE)

3. Treatment
• Sensitive to metronidazole, clindamycin & cefoxitin
• Resistance to penicillin, some cephalosporins, and aminoglycosides
• Abscesses should be surgically drained.
Prevention
• In bowel surgery, perioperative cefoxitin can reduce the frequency of
postoperative infections.
• No vaccine is available.

4. Fusobacterium
• Obligately anaerobic filamentous GNR.
• Commensals of the mouth, colon, and female genital tract.
• F. necrophorum tends to cause infection rarely in younger individuals
and F. nucleatum in older patients.
• Clinical spectrum is ranging from local, non-severe infections, such as
sinusitis or pharyngitis, to abscess formation, severe neck pain, patient
appears toxic and life-threatening infections.

5. Lab Diagnosis:
• Anaerobic gram-negative bacilli, non-sporulating, slender cells with
tapered ends or pleomorphism.
• Fusobacterium spp. are difficult to culture, as they only grow under
strict anaerobic conditions.
• Most species are Indole positive
• Oxidase negative
Treatment:
• Sensitive to both kanamycin and colistin

6. Porphyromonas
• Anaerobic GNR, part of the salivary microbiome
• Usually grows as pigmented colonies
• Important pathogen associated with human periodontal disease.
• Porphyromonas gingivalis can produce various virulence factors to
evade the host immune defense system and destroy host periodontal
tissues.
• Lipopolysaccharide, gingipains, fimbriae/pili, collagenase,
(erythrocyte) lectins, capsule, protease, and superoxide dismutase

7. Lab diagnosis
• Porphyromonas spp. tend to form smaller colonies.
• Shorter rods or coccobacilli on Gram stain
Fig (A) and (B): Dark Pigmented Colonies of Porphyromonas Gingivalis

8. Prevotella
• Non-motile, short GNR, anaerobic oral microbiome.
• Largest single bacterial group reported from the rumen of cattle and
sheep under most dietary regimes.
• Produce capsule & succinic acid which inhibits phagocytosis.
• Can cause periodontitis, bacterial vaginosis, rheumatoid arthritis,
metabolic disorders and low‐grade systemic inflammation.
• Prevotella intermedia is closely associated with periodontal disease.
Lab Diagnosis
Culture: P. melaninogenica produces characteristic black
indole positive colonies

9. Treatment
• Sensitive to metronidazole and clindamycin
• Resistance to aminoglycosides, aztreonam, trimethoprim,
sulfonamides and fosfomycin
• Abscesses should be surgically drained.
Prevention
• Prevention of Prevotella infections centers on perioperative
administration of a cephalosporin, for abdominal or pelvic surgery.
• No vaccine is available.

10. Veillonella
• Nonmotile, gram-negative diplococci.
• Part of the normal flora of the mouth (dental plaque), gastrointestinal
tract, and vagina.
• Produce a highly endotoxic lipopolysaccharide.
• Rare causes of serious infections such as meningitis, osteomyelitis,
prosthetic joint infection, pleuropulmonary infection, endocarditis, and
bacteraemia.

11. Lab diagnosis
Specimens:
• Blood, pus from abscess, pulmonary secretions etc.
Direct microscopy:
• Gram smear, very small gram negative cocci in clumps, pairs or short chain.
Culture: Small round colonies with raised centers on enriched blood media (brain-
heart infusion and trypticase soya agar) supplemented with sheep blood.
Biochemical tests: Oxidase and catalase negative.
Treatment: Sensitive: Chloramphenicol, clindamycin, metronidazole, meropenem,
imipenem, piperacillin, cefoxitin
Resistant: penicillin, vancomycin, ciprofloxacin and tetracycline.
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