Gram Negative Anaerobes

Question 1

Describe the characteristics of Bacteroides Fragilis

Answer 1

Non spore forming
Non motile
Enriched media required
Normal flora of GI
Protect from invasion of other organisms

Question 2

If B.Fragilis is normal flora in gut how does it cause pathology?

Answer 2

When it gets out of it’s normal niche

Question 3

What is the hallmark clinical sign of B.Fragilis pathology?

Answer 3

Abscess formation -> mixed infections of aerobes and anaerobes

Question 4

Describe the abscess formed by B.fragilis

Answer 4

Inflammatory response to infection

Encapsulated pus of PMN, fibrin, debris, necrotic tissue

Question 5

What are the virulence factors of B.Fragilis?

Answer 5

Polysaccharide capsule - adheres to peritoneal cavity ; resist phagocytosis,
O2 Tolerance: SOD, catalase

Question 6

What is the defective endotoxin of B.Fragilis?

Answer 6

Same endotoxin as e.coli but defective -> no toxic effects as E.coli endotoxin

Question 7

Where is B.fragilis most commonly found in clinical infections?

Answer 7

Intraabdominal Infections
Wound Infections (stool contaminates open wound usually)
Aspiration pneumonia\
Female Genital Tract

Question 8

What are the most common aerobic and anaerobic pathogens found in intraabodimnal infections?

Answer 8

Aerobic: E.Coli
Anaerobic: Bacteroides (Fragilis)

Question 9

what is fournier gangrene?

Answer 9

Intraabdominal infection that spreads down into scrotum, leg, buttocks

Question 10

How does diabetic food arise?

Answer 10

Ulcers -> get infected-> disseminates to bone -> get lots of bugs -> mainly Staph Aureus

Question 11

Describe Prevotella

Answer 11

Gram Negative Strict Anaerobes
Requires enriched media
Non-motile
Non-encapsulated
Found in mouth, GI, pelvis

Question 12

What is prevotella inifections associated with?

Answer 12

Abscess formation in brain

Question 13

Which species of prevotella are found in femal genital tract infections?

Answer 13

P.bivia

P.disiens

Question 14

Which species of prevotella are found in the oral cavity, urogenital and GI tract?

Answer 14

P.melaninogenica

Question 15

What are some other important gram negative anaerobes?

Answer 15

Porphyromonas

Fusobacterium- nucleatum, necrophorum

Question 16

Which fusobacterium causes Lemierre’s syndrome?

Answer 16

F.Necrophorum -> peritonsilar abscess; highly virulent wiht potent endotoxin

Question 17

What abx are used to generally treat anaerobes?

Answer 17

Metronidazole
Ampicillin/Sulbactam
Piperacillin/tazobactam
Carbapenem
Chloramphenicol

Question 18

Which gram negative anaerobes are most resistant to abx?

Answer 18

B.Fragilis

Question 19

Why are gram negative anaerobes highly resistant?

Answer 19

Make B-lactamase => thus use B-lactamase inhbiitor (ex: ampicillin and piperacillin effective)