Aggregatibacter aphrophilus – Bacteria and Endocarditis
Aggregatibacter aphrophilus is a gram-negative bacterium found in normal oral flora that can rarely but seriously cause infections such as infective endocarditis.
Things worth knowing about "Aggregatibacter aphrophilus"
Aggregatibacter aphrophilus is a gram-negative bacterium found in normal oral flora that can rarely but seriously cause infections such as infective endocarditis.
What is Aggregatibacter aphrophilus?
Aggregatibacter aphrophilus is a gram-negative, facultatively anaerobic rod-shaped bacterium that is part of the normal flora of the human oral cavity and pharynx. Previously classified as Haemophilus aphrophilus, it was reclassified into the genus Aggregatibacter following taxonomic revisions. The organism belongs to the HACEK group – a collection of fastidious microorganisms known for causing difficult-to-diagnose infections of the heart and other organs.
Occurrence and Transmission
Aggregatibacter aphrophilus is a commensal organism residing in the oral cavity without typically causing harm. Infection occurs when the bacterium enters the bloodstream, which can happen through:
- Dental procedures or tooth extractions
- Poor oral hygiene and periodontal disease
- Injuries to the oral mucosa
- Surgical procedures in the head and neck region
Individuals with pre-existing heart valve disease or congenital heart defects are at significantly higher risk of developing serious infections.
Clinical Manifestations and Symptoms
The most clinically significant disease caused by Aggregatibacter aphrophilus is infective endocarditis – an infection of the inner lining of the heart, particularly the heart valves. Other possible infections include:
- Brain abscesses
- Periodontal infections
- Septicemia (bloodstream infection)
- Osteomyelitis (bone infection)
- Pneumonia (rarely)
Endocarditis caused by Aggregatibacter aphrophilus typically presents with a subacute course and may include:
- Persistent fever
- Night sweats and chills
- Fatigue and general malaise
- Unexplained weight loss
- New or changing heart murmurs
- Joint and muscle pain
Diagnosis
Diagnosing Aggregatibacter aphrophilus infections can be challenging due to the slow-growing nature of the bacterium. Key diagnostic steps include:
- Blood cultures: The gold standard; multiple samples over time are required for reliable detection
- Echocardiography: Cardiac ultrasound to detect vegetations (bacterial deposits) on heart valves
- Molecular methods: PCR-based assays for direct detection of bacterial DNA
- Biochemical identification: Laboratory tests to precisely identify the bacterial strain
Extended incubation periods in blood culture systems (up to 14 days) highlight the importance of early clinical suspicion.
Treatment
Infections caused by Aggregatibacter aphrophilus are treated with antibiotics. The bacterium is generally susceptible to:
- Beta-lactam antibiotics (e.g., ampicillin, amoxicillin)
- Third-generation cephalosporins (e.g., ceftriaxone)
- Fluoroquinolones (e.g., ciprofloxacin)
For infective endocarditis, combination therapy with a beta-lactam antibiotic and an aminoglycoside (e.g., gentamicin) is often recommended, typically for several weeks. The duration and regimen depend on the severity of infection and the structures involved. In severe cases with significant valve damage, surgical intervention may be required.
Prevention
Preventive measures against Aggregatibacter aphrophilus infections include:
- Thorough oral hygiene and regular dental check-ups
- Treatment of periodontal disease and dental infections
- Antibiotic prophylaxis before dental procedures for high-risk patients (e.g., those with valvular heart disease) according to current clinical guidelines
References
- Patel R. - HACEK group Endocarditis. In: Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th edition. Elsevier, 2020.
- Murdoch DR et al. - Clinical Presentation, Etiology, and Outcome of Infective Endocarditis in the 21st Century. Archives of Internal Medicine, 2009. PubMed PMID: 19858436.
- European Society of Cardiology (ESC) - Guidelines on the management of infective endocarditis. European Heart Journal, 2023. https://www.escardio.org
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