Streptococcus pneumoniae is a topic covered in the Johns Hopkins Antibiotic (ABX) Guide.

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MICROBIOLOGY

  • Aerobic, Gram-positive diplococcus with capsule.
  • Grows on blood agar.
  • Capsular swelling w/ application of Quelling antisera.
  • Serotypes: immunity is serotype-specific.
    • Abx resistance is often serotype-specific.
    • Serotype 19A has emerged as predominant pathogen following increased immunization.
  • Minimum inhibitory concentration (MIC) to penicillin (mcg/mL) breakpoints for non-CNS specimens.
    • Susceptible: 2 mcg/mL
    • Intermediate: 4 mcg/mL
    • Resistant: 8 mcg/mL
    • Previously were determined solely on the basis of possible meningeal disease.
      • New breakpoints above are based on anticipated respiratory or non-CNS isolates.
      • Susceptible breakpoint for meningitis caused by S. pneumoniae remains unchanged
        • S= 0.06 mcg/mL
        • I = 0.12 - 1.0 mcg/mL
        • R ≥ 2 mcg/mL
      • This now means that >95% of strains are sensitive to penicillin, and penicillin is the preferred drug.
  • Penicillin resistance is increasing due to "replacement strains" associated with extensive use of Prevnar (PCV-7, now PCV-13) vaccine with emergence of 19A strain and more recently serotypes 6C and 35. These serotypes are relatively non-susceptible to penicillin.

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Last updated: December 7, 2015