TABLE 1.
Susceptibilities of S. pneumoniae by disk diffusion and Etest according to mechanism of macrolide resistance
| Resistance mechanism | Etest MICs (μg/ml) of:
|
Clindamycin 2-μg disk inhibitory zone range (mm) | |||||
|---|---|---|---|---|---|---|---|
| Clarithromycin
|
Clindamycin
|
||||||
| Range | MIC50 | MIC90 | Range | MIC50 | MIC90 | ||
| mefE+(n = 125) | 2–128 | 4 | 32 | ≤0.25 | ≤0.25 | ≤0.25 | 21–31 |
| ermB+(n = 70) | 2–>256a | >256 | >256 | >256 | >256 | >256 | 6b |
| Neither (n = 3) | 4–>256 | — | — | 0.25–64 | — | — | 6b–22 |
a
Two ermB+ isolates had high-level resistance to clindamycin (>256 μg/ml) but clarithromycin MICs were 2 μg/ml.
b
The width of the disk is 6 mm. There was no evidence of inhibition surrounding it.