- 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.
- Minimum Inhibitory Concentration (MIC) to penicillin (mcg/mL) breakpoints for non-CNS specimens.
- Susceptible: (2)
- Intermediate: (4)
- Resistant: (8)
- Previously S = 0.06, I = 0.12-1.0 and R ≥ 2 breakpoints 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). 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 7 (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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