Infectious Disease and Microbiology - Bilophila wadsworthia

Basics

Bilophila wadsworthia is an anaerobic Gram-negative bacillus that can be part of the gastrointestinal microbiota. When it causes disease, it is commonly recovered as part of a polymicrobial infection, particularly in intra-abdominal infections.

Microbiologic Characteristics

Bilophila wadsworthia is:

• Gram negative

• Bacillary in shape

• Anaerobic

Because it requires anaerobic conditions for growth, appropriate specimen collection and anaerobic culture techniques are important for laboratory recovery.

Epidemiology

B. wadsworthia is most often isolated together with other aerobic and anaerobic organisms rather than as the sole pathogen.

Its clinical importance is greatest in infections involving the gastrointestinal tract and other normally sterile sites contaminated by intestinal organisms.

Clinical Infections

Intra-abdominal Infection

A major clinical association is peritonitis secondary to appendicitis.

Disruption or perforation of the gastrointestinal tract can allow the organism to enter the peritoneal cavity along with other members of the intestinal flora.

The resulting infection is commonly polymicrobial.

Bacteremia

B. wadsworthia may occasionally enter the bloodstream and cause bacteremia.

This is more likely in the setting of:

• Severe intra-abdominal infection

• Disruption of gastrointestinal integrity

• Abscess formation

• Significant underlying illness

Liver Abscess

The organism has also been associated with hepatic abscesses, usually in the context of infection arising from the gastrointestinal or biliary system.

Such infections may contain multiple aerobic and anaerobic organisms.

Diagnosis

Diagnosis is established by:

Anaerobic culture

Appropriate collection and transportation of specimens are essential because exposure to oxygen can reduce the recovery of anaerobic bacteria.

Suitable specimens may include:

• Peritoneal fluid

• Abscess material

• Blood

• Surgically obtained tissue or fluid

Treatment

Metronidazole

Metronidazole has activity against many clinically important anaerobic organisms and may be used when B. wadsworthia is susceptible.

Clindamycin

Clindamycin has also historically been used for anaerobic infections, although susceptibility should be considered because resistance among anaerobic organisms can vary.

Additional Antibiotic Options

Other agents with anaerobic activity include:

• Imipenem

• Meropenem

• Piperacillin-tazobactam

• Ticarcillin-clavulanate

• Cefoxitin

For serious polymicrobial intra-abdominal infections, therapy should provide appropriate coverage for the other expected organisms as well.

Source Control

Antibiotics alone may not be sufficient when infection is associated with:

• Perforated appendicitis

• Peritonitis

• Intra-abdominal abscess

• Liver abscess

Drainage, surgery, or other appropriate source-control procedures may therefore be necessary.

Exam Essentials

Organism:

→ Bilophila wadsworthia

Microbiology:

→ Anaerobic Gram-negative bacillus

Typical setting:

→ Mixed or polymicrobial infection

Major infections:

→ Peritonitis after appendicitis, bacteremia, liver abscess

Diagnosis:

→ Anaerobic culture

Treatment:

→ Metronidazole or another active anaerobic agent

Other options:

→ Carbapenems, piperacillin-tazobactam, cefoxitin

Important management principle:

→ Antibiotics + source control when an abscess or perforated intra-abdominal process is present

Key clinical pearl: Bilophila wadsworthia should be considered an anaerobic component of polymicrobial intra-abdominal infections rather than a common isolated pathogen.