Table 1.

Streptococcus strains characterized according to their macrolide resistance determinants and MICs

Organism GeneanMIC (μg/ml)
Telithromycin (HMR 3647) Erythromycin Clindamycin
Range 50% 90% Range 50% 90% Range50% 90%
S. pyogenes S20 0.008–0.063 0.016 0.063≤0.031–0.25 0.063 0.125≤0.031–0.125 0.063 0.063
erm(TRi) 42 0.031–0.250.063 0.063 0.5–>64 4 8 0.063–>64 0.1250.25
erm(TRc) 10.25 >64>64
erm(Bi) 2 0.5–1>64 0.25
erm(Bc) 6 4–64 864 >64 >64 >64>64 >64 >64
mef(A) 58 0.063–0.5 0.5 0.54–16 8 8 ≤0.031–0.125 0.063 0.063
erm(TRi) + mef(A) 10.25 8 0.063
erm(Bi) + mef(A)1 4 >64 0.25
bsc S 10 ≤0.008–0.25 0.0160.031 ≤0.031–0.125 0.063 0.063 ≤0.031–0.1250.125 0.125
mef(A) 18 0.031–0.50.25 0.5 1–8 4 8 0.063–0.125 0.1250.125
bsg S 11 ≤0.008–0.031 0.0310.031 0.063–0.25 0.063 0.063 ≤0.031–0.250.063 0.125
erm(TRi) 180.031–0.063 0.063 0.063 1–>64 4 640.063–0.5 0.125 0.5
S. pneumoniae S 10 ≤0.008–0.031 ≤0.008 0.031≤0.031–0.063 ≤0.03 ≤0.031 ≤0.031–0.063 0.0630.063
erm(Bc) 20≤0.008–0.25 0.063 0.25 64–>64 >64 >640.25–>64 >64 >64
mef(A) 80.063–0.5 0.125 0.5 1–4 2 4 0.063–0.1250.063 0.125
Novel phenotypeb 9 0.031–0.125 0.063 0.125 64–>64 >64>64 0.5–4 1 4
MIC (μg/ml)
AzithromycinClarithromycin SpiramycinQuinupristin-dalfopristin (RP59500)
Range50% 90% Range 50% 90% Range 50%90% Range 50% 90%
0.063–0.5 0.125 0.25≤0.031–0.125 0.031 0.0630.25–1 0.25 0.5 0.25–10.5 1
0.5–>64 16 32 0.25–>64 22 0.5–64 1 8 0.25–1 0.5 0.5
>64>64 64 0.25
>64>64 >64 0.5
>64 >64 >64>64 >64 >64>64 >64 >64 0.5–10.5 1
1–16 4 8 1–8 4 80.125–2 0.25 0.5 0.25–1 0.5 0.5
8 8 0.50.25
>64>64 >64 0.5
0.063–0.25 0.125 0.25≤0.031–0.063 0.031 0.063 0.125–0.5 0.250.5 0.5–2 1 2
1–4 4 40.25–4 4 4 0.125–1 0.5 10.5–4 1 2
0.125–1 0.125 0.125≤0.031–0.25 ≤0.031 0.063 0.125–1 0.50.5 0.5–1 1 1
4–>64 16 >640.5–>64 1 8 0.5–4 2 4 1–21 1
≤0.031–0.125 0.125 0.125 ≤0.031 ≤0.031 ≤0.0310.125–0.25 0.125 0.25 0.5–2 1 2
>64 >64 >64 8–>64>64 >64 16–>64 >64 >64 0.5–42 4
1–4 2 4 1–4 2 40.125–0.25 0.125 0.25 0.5–1 1 1
32–>64 64 >64 16–>64 >64 >64>64 >64 >64 2–44 4
  • a i, inducible; c, constitutive; S, erythromycin-susceptible strain; erm = erythromycin ribosome methylation genes; mef, macrolide eflux genes.

  • b See text for details.