Table 1.

Susceptibilities of S. pneumoniae by disk diffusion and Etest according to mechanism of macrolide resistance

Resistance mechanismEtest MICs (μg/ml) of:Clindamycin 2-μg disk inhibitory zone range (mm)
ClarithromycinClindamycin
RangeMIC50MIC90RangeMIC50MIC90
mefE+ (n = 125)2–128432≤0.25≤0.25≤0.2521–31
ermB+ (n = 70)2–>256a>256>256>256>256>256 6b
Neither (n = 3)4–>2560.25–646b–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.