What is the most common causative agent in acute bacterial endocarditis?

From the Guidelines

The most common causative agent in acute bacterial endocarditis is Staphylococcus aureus, as it accounts for approximately 30-40% of all cases of infective endocarditis and is the predominant organism in acute presentations 1. This aggressive pathogen has several virulence factors that allow it to adhere to heart valves, form biofilms, and cause rapid valve destruction. According to the 2015 guidelines from the American Heart Association, 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.

Some key points to consider in the management of acute bacterial endocarditis include:

• The infection progresses rapidly, often causing high fevers, new heart murmurs, embolic phenomena, and valve destruction within days to weeks if untreated.
• Treatment typically involves 4-6 weeks of intravenous antibiotics, usually with an anti-staphylococcal penicillin (such as nafcillin or oxacillin) or vancomycin for methicillin-resistant strains, often combined with gentamicin for the first few days.
• Early surgical intervention may be necessary in cases with complications such as heart failure, persistent bacteremia, or large vegetations with embolic risk.
• The 2008 guidelines from the American College of Cardiology/American Heart Association also highlight the importance of identifying the causative organism to guide antimicrobial therapy, with Staphylococcus aureus being a frequent cause of infective endocarditis in patients with insulin-dependent diabetes mellitus and in cases of tricuspid valve infection 1.

Overall, Staphylococcus aureus is the most common causative agent in acute bacterial endocarditis, and its management requires prompt and effective antimicrobial therapy, as well as consideration of potential complications and the need for early surgical intervention 1.

From the Research

Causative Agents in Acute Bacterial Endocarditis

• The most common causative agents in acute bacterial endocarditis include:
  • Staphylococcus aureus, which is the most common microorganism, found in 54.3% of studies 2
  • Viridans group streptococci (VGS) 2
  • Coagulase-negative staphylococci (CoNS) 2
  • Enterococcus spp 2
  • Streptococcus bovis 2

Specific Causative Agents

• Staphylococcus aureus is the leading cause of infective endocarditis in the 21st century, found in 55.4% of studies using Duke's criteria for diagnosis 2
• Viridans streptococci, enterococci, and coagulase-positive staphylococci are also common causes of bacterial endocarditis 3, 4

Treatment of Infective Endocarditis

• The treatment of infective endocarditis depends on the identity and antibiotic susceptibility of the infecting organism, the type of cardiac valve involved, and characteristics of the patient 3
• Antibiotic therapies, such as aqueous penicillin or ceftriaxone, are effective for most infections caused by streptococci 3, 4
• Vancomycin should be substituted for penicillin when high-level resistance is present 3