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A Case Report of Penicillin-Tolerant Streptococcus mitis Endocarditis Chang-Hua Chen, MD, MSc, PhD

Chang-Hua Chen1

  • 1Department of Internal Medicine, Changhua Christian Hospital, Taiwan.

The Heart Surgery Forum
|February 28, 2018
PubMed

Insights

Serum inhibition tests do not reliably predict treatment success for Streptococcus mitis endocarditis. Penicillin-tolerant S. mitis endocarditis can resolve with high-dose penicillin, despite in vitro test results.

Area of Science:

  • Infectious Diseases
  • Cardiology
  • Microbiology

Background:

  • Streptococcus mitis endocarditis (S. mitis) is a serious infection.
  • Predicting treatment outcomes for S. mitis endocarditis can be challenging.
  • The role of in vitro tests like serum inhibition tests (SIT) and serum bactericidal tests (SBT) in guiding therapy is unclear.

Observation:

  • An 84-year-old male presented with endocarditis caused by penicillin-tolerant S. mitis.
  • In vitro testing revealed high serum inhibitory and bactericidal levels, with a high SIT/SBT ratio, consistent with penicillin tolerance.
  • The patient received a 42-day course of high-dose intravenous penicillin.

Findings:

  • The patient achieved a good clinical recovery following treatment.
  • In vitro SIT and SBT results did not accurately predict the successful medical treatment outcome.
  • The SIT/SBT ratio indicated penicillin tolerance, yet high-dose penicillin therapy was effective.

Implications:

  • In vitro tests may not be reliable predictors of treatment failure in penicillin-tolerant S. mitis endocarditis.
  • Physicians must carefully consider surgical intervention indications, even with seemingly unfavorable in vitro test results.
  • Clinical judgment remains paramount in managing S. mitis endocarditis, particularly in cases of penicillin tolerance.

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