From the Guidelines
Infective endocarditis is primarily caused by microbial infection of the heart valves or endocardial surface, with bacteria being the most common pathogens, and the most recent evidence suggests that coagulase-negative staphylococci, Staphylococcus aureus, and Enterococcus species are the most frequent causative organisms 1. The etiology of infective endocarditis involves a complex interplay of host and microbial factors, with the majority of cases being due to streptococcal and staphylococcal organisms.
- The pathogenesis involves initial damage to the endocardial surface, followed by platelet and fibrin deposition creating a sterile vegetation.
- When bacteremia occurs, microorganisms can adhere to this vegetation, multiply, and form an infected vegetation.
- Risk factors include pre-existing cardiac conditions (valvular disease, prosthetic valves, congenital heart defects), intravenous drug use, indwelling catheters, recent dental or surgical procedures, and immunocompromised states.
- The increasing prevalence of healthcare-associated infections has shifted the epidemiology, with S. aureus now being the most common causative organism in many regions.
- Understanding the etiology is crucial for appropriate empiric antibiotic selection while awaiting blood culture results, which should include coverage for both streptococci and staphylococci in most cases, as recommended by guidelines 2. The most recent study on the topic, published in 2023, highlights the diversity of pathogens involved in prosthetic valve endocarditis, including coagulase-negative staphylococci, Staphylococcus aureus, Enterococcus species, and Gram-negative bacilli 1.
- This study emphasizes the importance of molecular biological detection methods, such as polymerase chain reaction (PCR) or whole genome analyses, in identifying the causative organism and guiding antibiotic therapy.
- The use of these methods can improve the diagnosis and treatment of infective endocarditis, particularly in cases where blood cultures are negative.
- The study also highlights the need for a comprehensive approach to the diagnosis and management of infective endocarditis, including the use of epidemiological data, clinical presentation, and laboratory results to guide antibiotic selection and treatment.
From the Research
Etiology of Infective Endocarditis
The etiology of infective endocarditis (IE) is complex and involves various microorganisms. According to the available evidence, the most common causative agents of IE are:
- Staphylococcus aureus, which was found to be the most common microorganism in 54.3% of studies 3
- Viridans group streptococci (VGS), which are also a common cause of IE 4, 5, 6
- Coagulase-negative staphylococci (CoNS) and Enterococcus spp, which are also among the most common causes of IE 3
- Streptococcus bovis, which is another common cause of IE 3
Penicillin-Resistant Viridans Group Streptococci
Penicillin-resistant VGS are a rare but challenging cause of IE. Studies have shown that:
- IE caused by penicillin-resistant VGS is rare, accounting for only 0.58% of streptococcal IE cases 4
- The majority of penicillin-resistant VGS isolates belong to the S. mitis group 4
- Antibiotic combination regimens, including beta-lactams, are effective in managing IE caused by penicillin-resistant VGS 4, 5, 6
- Vancomycin-based regimens may also be effective in treating IE caused by highly penicillin-resistant VGS 6
Other Causative Agents
Other microorganisms, such as Staphylococcus aureus, CoNS, and Enterococcus spp, are also common causes of IE. The epidemiology of IE varies depending on the population subgroup, with S. aureus being the most common pathogen in almost all subgroups, except for patients with implantable devices, prosthetic valves, or immunocompromised non-HIV, as well as in the sub-group from Asia 3.