Gram-Negative Anaerobes: Bacteroides, Prevotella, Porphyromonas, Fusobacteria. Flashcards
(4 cards)
Bacteroides fragilis
Bacteroides fragilis is an anaerobic gram-negative rod that is part of normal gut flora. It causes intra-abdominal abscesses, peritonitis, and wound infections, often after bowel surgery or perforation. It has a polysaccharide capsule that promotes abscess formation and helps evade the immune system. It produces beta-lactamase, making it resistant to penicillin. It is the most common anaerobe isolated from clinical specimens. Treatment includes metronidazole, carbapenems, or beta-lactam/beta-lactamase inhibitor combinations.
Prevotella species
Prevotella are anaerobic gram-negative rods found in the oral cavity, GI tract, and female genital tract. They are involved in dental infections (periodontitis), aspiration pneumonia, PID, and tubo-ovarian abscesses. They produce black-pigmented colonies on blood agar. Prevotella species are often isolated with other anaerobes in mixed infections. Treatment includes metronidazole or clindamycin.
Porphyromonas species
Porphyromonas are black-pigmented, anaerobic gram-negative rods primarily found in the oral cavity. They are associated with periodontal disease and dental abscesses. They are also implicated in aspiration pneumonia and chronic sinusitis. Porphyromonas are sensitive to metronidazole and resistant to aminoglycosides. They produce proteolytic enzymes that contribute to tissue destruction.
Fusobacterium species
Fusobacteria are anaerobic gram-negative rods with pointed ends. Found in the mouth, colon, and female genital tract. They cause dental infections, brain abscesses, aspiration pneumonia, and Lemierre’s syndrome (caused by Fusobacterium necrophorum)—characterized by sore throat, internal jugular vein thrombosis, and septic emboli to lungs. They produce endotoxin (lipopolysaccharide) and proteolytic enzymes. Treatment includes metronidazole or beta-lactam/beta-lactamase inhibitors.
