Editors' ChoiceCardiology

A Change of Heart

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Science Translational Medicine  04 May 2011:
Vol. 3, Issue 81, pp. 81ec65
DOI: 10.1126/scitranslmed.3002571

In 2007, the American Heart Association (AHA) updated their recommendations for antimicrobial prophylaxis for heart disease patients undergoing surgery. Given that infection of the heart valves (infective endocarditis) often occurs independently of surgical procedures, the guidelines contained substantive changes recommending that only a high-risk group of heart disease patients should receive antimicrobials before surgery. A new study by Veloso et al. now provides experimental evidence that not only high-grade bacterial infections in the bloodstream (such as those that might be acquired during surgery) but also long-term exposure to low-grade infections (such as those due to commensal bacteria) can boost the risk for infective endocarditis.

To demonstrate that low-grade bacteremia is a risk factor for developing infective endocarditis, the authors inoculated rats with equal concentrations of Streptococcus intermedius or S. gordonii (both oral commensal bacteria) or Staphylococcus aureus. Bacteria were administered either by a single bolus (simulating a high-grade bacterial infection) or by continuous infusion over 10 hours (to mimic longer-term, low-grade exposure to bacterial infection). To determine the concentration of bacteria in the blood, samples were taken at 1 min and 2 hours in the bolus group, and at 2 and 6 hours in the continuous infusion group. After 24 hours, the rats were killed and the number of bacterial colony-forming units in the heart valves and spleen were counted.

The authors found that both streptococci and staphylococci bacteria administered by continuous infusion were able to infect the heart valves and spleen of rats as efficiently as bacteria administered by a single bolus. This suggests that the risk of infective endocarditis is similar whether from a transient high-grade bacteremia or from long-term exposure to a low-grade infection. Although it is not clear how closely this rat model of infective endocarditis mimics the human disease, the study by Veloso et al. supports the AHA’s view that low-grade cumulative exposure to commensal organisms is a risk factor for infective endocarditis. This rat model may help to further boost our understanding of the causes of infective endocarditis and its prevention.

T. R. Veloso et al., Induction of experimental endocarditis by continuous low-grade bacteremia mimicking spontaneous bacteremia in humans. Infect. Immun. 79, 2006–2011 (2011). [PubMed]

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