From the Guidelines
Staphylococcus aureus tends to cause early onset endocarditis, while streptococci are more commonly associated with late onset endocarditis, due to differences in their virulence factors and pathogenic mechanisms. According to the most recent guidelines, for patients with acute clinical presentations of native valve infection, coverage for S aureus, β-hemolytic streptococci, and aerobic Gram-negative bacilli is reasonable 1. This is because Staphylococcus aureus possesses aggressive adhesion proteins like fibronectin-binding proteins and clumping factors that allow it to rapidly attach to damaged heart valves or prosthetic materials immediately after surgery or device placement. In contrast, streptococci (especially viridans group) have less aggressive virulence factors but can gradually accumulate on heart valves over time through everyday activities like dental procedures or normal oral flora disturbances.
Some key points to consider in the management of endocarditis include:
- The majority (80%) of cases of endocarditis are due to streptococcal and staphylococcal organisms 1
- Staphylococcus aureus is the most frequent organism in endocarditis resulting from intravenous drug abuse, and is also a frequent cause of infective endocarditis in patients with insulin-dependent diabetes mellitus 1
- In “early” prosthetic valve endocarditis, usually defined as endocarditis during the first 2 months after surgery, Staphylococcus epidermidis is the predominant offending organism 1
- Late-onset prosthetic valve endocarditis follows the profile of native valve endocarditis, that is, streptococci (viridans) and staphylococci 1
The most recent guidelines recommend that for patients with culture-negative endocarditis, an evaluation of epidemiological factors, history of prior infections, exposure to antimicrobials, clinical course, severity, and extracardiac sites of infection should be performed 1. Additionally, consultation with an infectious diseases specialist to define the most appropriate choice of therapy in patients with culture-negative endocarditis is recommended 1. Overall, the management of endocarditis should be guided by the identification of the causative organism, and the most recent guidelines should be consulted for specific recommendations on antimicrobial therapy and management of complications.
From the Research
Causes of Early and Late Onset Endocarditis
- Staphylococci and streptococci are the most common causes of infective endocarditis, accounting for 75% of cases 2.
- Staphylococcus aureus is a common cause of endocarditis, particularly in patients with no preceding heart condition or in intravenous drug users 3.
- Viridans streptococci are more commonly associated with subacute endocarditis, which may present as late onset endocarditis 3.
Treatment of Endocarditis
- The treatment of infective endocarditis depends on the causative microorganism and its antibiotic susceptibilities, as well as whether the involved valve is native or prosthetic 2, 4.
- Staphylococcal endocarditis is typically treated with anti-staphylococcal penicillins, such as nafcillin or oxacillin, or vancomycin for methicillin-resistant isolates 2, 4.
- Streptococcal endocarditis is typically treated with penicillin or ampicin, often in combination with an aminoglycoside 2.
Comparison of Antibiotic Regimens
- Several studies have compared different antibiotic regimens for the treatment of infective endocarditis, but the evidence is limited and of low to very low quality 5, 6.
- These studies have found no conclusive differences between antibiotic regimens in terms of cure rates or other relevant clinical outcomes 5, 6.
- The choice of antibiotic regimen should be individualized based on the specific circumstances of each patient, including the causative microorganism, antibiotic susceptibilities, and underlying health conditions 4, 3.