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- Aerobic, Gram-positive diplococcus with a 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 and 19F 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 the emergence of 19A strain and more recently serotypes 6C and 35. These serotypes are relatively nonsusceptible to penicillin.