Aanaerobic Gram-negative rods (Bacteroides, Fusobacterium, Prevotella, Porphyromonas) and associated infections

Question 1

General Characteristics of Anaerobes:

Answer 1

Rod shape
some elongated while some small
part of the normal flora

Question 2

What metabolic enzymes are lacking in anaerobes?

Answer 2

Cytochrome system for oxygen metabolism

Superoxide Dismutase: 2O2 + 2H+ → O2 + H2O2

Catalase (partly): 2H2O2 → 2H2O + O2

Peroxidase (partly): H2O2 + H2R → 2H2O + R

Question 3

Where and what genus do we have in our various flora

Answer 3

aerobe/anaerobe ratio
1:10 Oral: Bacteroides, fusobacterium, porphyromonas, and lactobacillus.

1: 1000 Colon: bacteroids, porphyromonas, clostridium, bifidobacterium, fusobacterium, lactobacillus
10: 1 skin: prevotella, bacteroids, and Propionibacterium

x/x (varies) vagina: Prevotella, lactobacillus, and bifidobacterium.

Question 4

Leading cause of endogenous infection

Answer 4

Poly-microbial infection

Complex pathogenesis
Predisposing factors- anaerobes are potentially pathogenic when displaced from normal environment and implanted in dead or dying tissues

Conditions when O2 is low: shock, angiopathy, DM

“Cut the barrier”: aspiration, operation, trauma

Question 5

General Laboratory Diagnosis

Answer 5

Anaerobic conditions are required for sample collection, culturing and identification.

Question 6

Antibiotics Treatment

Answer 6

Only given after MIC determination; can use Metronidazole (effective against anaerobes), Clindamycin, Imipenem, Penicillin, Chloramphenicol.

Question 7

Associated diseases of mentioned anaerobic rods

Answer 7

Bacteroides fragilis (GI): intra abdominal infection

Prevotella bivia: Pelvic abscesses

Porphyromonas spp.: Periodontitis, orofacial abscess

F. nucleatum: Mixed pyogenic infection (mouth, colon, vagina)

F. perodonticum: Lower respiratory tract infection

Question 8

Specific features of bacteroids (fragilis and distanosis):

Answer 8

Bacteroides (B. fragilis, B. distanosis…)

Capsular polysaccharide

Hyaluronidase, fibrinolysin, DNase, heparinase

Toxin (heat-labile zinc metalloprotease)

Question 9

Specific features of Porphyromonas (P. asaccharolytica, P. gingivalis)

Answer 9

Trypsin-like activity

Collagenase

Question 10

Specific features of Prevotella (P. disiens, P. bivia…)

Answer 10

IgA protease
Collagenase,
fibrinolysin

Question 11

Specific features of Fusobacterium (F. nucleatum, F. varium)

Answer 11

Fusobacterium nucleatum in combination with oral spirochates (Treponema vincentii and
others) causes the fusospirochaetal infections

Plaut-Vincent angina: ulcerative tonsillitis causing tissue necrosis often due to extension of
acute ulcerative gingivitis

Diagnosis- Giemsa stain preparation