Bacteroides fragilis: Characteristics & Infections

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Questions and Answers

Which of the following statements correctly describes a key characteristic differentiating Bacteroides fragilis from other gram-negative bacteria?

It frequently causes disease above the diaphragm, especially respiratory infections.
It possesses lipopolysaccharides that have little or no endotoxic activity. (correct)
It possesses lipopolysaccharides with potent endotoxic activity, similar to Enterobacteriaceae.
Its infections are primarily communicable, spreading through respiratory droplets.

What is the primary reason surgical drainage is considered essential in the treatment of Bacteroides fragilis abscesses?

To ensure antibiotics can effectively reach and penetrate the infected tissue. (correct)
To reduce the risk of the bacteria developing resistance to metronidazole.
To prevent the spread of the communicable bacteria to other organs.
To eliminate the foul-smelling exudates produced by the organism that interfere with healing.

In the context of a polymicrobial infection involving Bacteroides fragilis, which diagnostic approach would provide the most rapid and specific identification of the organism?

Proteomic tools, such as mass spectrometry, for protein profiling. (correct)
Gram staining to identify faint, slender, gram-negative rods amidst mixed flora.
Gas chromatography to detect characteristic short-chain fatty acids.
X-ray imaging to detect the presence of mixed anaerobic agents.

An immunocompromised patient develops a severe intra-abdominal infection post-surgery. Cultures reveal Bacteroides fragilis resistant to multiple antibiotics. Besides metronidazole, which alternative antibiotic regimen would be MOST appropriate?

Imipenem-cilastatin. (C) Signup and view all the answers

Bacteroides fragilis is identified as a causative agent in a patient presenting with necrotizing fasciitis. How does this infection typically originate?

From the patient's own endogenous flora gaining access to tissues, often from mucosal surfaces. (D) Signup and view all the answers

A researcher is investigating the virulence mechanisms of Bacteroides fragilis. What is the most accurate description of the role of the polysaccharide capsule in its pathogenicity?

The purified capsule alone is sufficient to induce abscess formation, acting as an endotoxin. (B) Signup and view all the answers

A patient presents with peritonitis and a suspected Bacteroides fragilis infection. Which of the following virulence factors is MOST likely contributing to the tissue damage?

Secretion of hyaluronidase, collagenase, and phospholipase. (D) Signup and view all the answers

If a laboratory is unable to culture Bacteroides fragilis from a clinical sample due to technical limitations, what alternative method could confirm its presence?

Using a PCR assay to detect specific Bacteroides fragilis DNA sequences. (C) Signup and view all the answers

While Bacteroides fragilis is often associated with intra-abdominal infections, it can also be found in lung abscesses. What percentage of lung abscess cases are estimated to involve Bacteroides fragilis?

About 25% (D) Signup and view all the answers

What is the MOST effective strategy to prevent Bacteroides fragilis infections in patients undergoing abdominal surgery?

Strict adherence to sterile surgical techniques and prophylactic antibiotics like cefoxitin if there is surgical contamination. (A) Signup and view all the answers

Flashcards

Bacteroides fragilis

Anaerobic gram-negative bacteria that can induce abscess formation, even with just the purified capsule.

Bacteroides fragilis Virulence Factors

Polysaccharide capsule and enzymes like hyaluronidase, collagenase, and phospholipase

Diagnosing Bacteroides fragilis

X-rays might indicate mixed anaerobic infection, gram stain shows slender rods, gas chromatography identifies short-chain fatty acids, and mass spectrometry identifies the organism via protein profiling.

Treating Bacteroides fragilis

Metronidazole is the first choice, but cefoxitin, cefotetan, ampicillin-sulbactam, impinem-cilastatin, and ticarcillin-clavulanate are alternatives.

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Infections caused by Bacteroides fragilis

Intra-abdominal infections such as lung, pelvic, and liver abscesses, and peritonitis.

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Study Notes

Bacteroides fragilis is an anaerobic gram-negative bacteria, appearing as slender rods or coccobacilli.
The purified capsule of Bacteroides fragilis can induce abscess formation.
Lipopolysaccharides in Bacteroides have minimal endotoxic activity.
These bacteria are part of the normal flora, causing disease upon tissue or blood access, often due to penetration or immunosuppression.
Infections are endogenous, originating from mucosal surfaces and are not communicable, leading to necrotizing fasciitis and bacteremia.

Virulence Factors

Polysaccharide capsule acts as an endotoxin.
Enzymes such as hyaluronidase, collagenase, and phospholipase contribute to tissue damage.
Enterotoxin-producing strains cause diarrhea in children and adults.

Diagnosis

X-rays of infections display mixed anaerobic agents, with exudate showing slender, gram-negative rods in mixed flora.
Gram stain reveals organisms alongside debris from nuclear acids.
Gas chromatography identifies short-chain fatty acids produced by the organism.
Proteomic tools like mass spectrometry are used for protein profiling.
Bacteroides fragilis is cultured on blood agar under anaerobic conditions, with lesions having foul-smelling exudates.

Treatment

Drug resistance is common in Bacteroides fragilis.
Metronidazole is the preferred antibiotic.
Alternative antibiotics include cefoxitin, cefotetan, ampicillin-sulbactam, imipenem-cilastatin, and ticarcillin-clavulanate.
Surgical drainage is essential for proper drug penetration.
Cefoxitin can be administered for surgical contamination.

Associated Infections

Frequently associated with intra-abdominal infections: localized, pelvic, and liver abscesses.
Found in about 25% of lung abscess cases.
Primarily causes disease below the diaphragm.
Can cause peritonitis.

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