TABLE 2.
Multipassage resistance selection results with S. pyogenes
| Strain | Antibiotica | Initial MIC (μg/ml) | Selected resistance
|
Retest MIC after 10 antibiotic-free subcultures
|
Detected resistance mechanismb | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| MIC | No. of passages | Retapamulin | Quin/Dalfo | Cephalexin | Erythromycin | Linezolid | Mupirocin | Vancomycin | ||||
| 2094 | Retapamulin | 0.016 | 0.125 | 26 | 0.125 | 0.5 | 0.5 | 4 | 1 | 0.25 | 0.5 | — |
| Quin/Dalfo | 0.25 | 2 | 38 | 0.016 | 0.5 | 1 | 8 | 4 | 0.25 | 0.5 | — | |
| Erythromycin | 4 | >64 | 4 | 0.03 | 0.5 | 1 | 16 | 2 | 0.25 | 0.5 | NT | |
| Mupirocin | 0.25 | 32 | 12 | 0.016 | 0.25 | 1 | 4 | 2 | 16 | 0.5 | — | |
| 2042 | Erythromycin | 4 | 32 | 4 | 0.03 | 0.125 | 1 | 16 | 1 | 0.125 | 0.5 | NT |
| Mupirocin | 0.125 | >32 | 9 | 0.03 | 0.125 | 1 | 8 | 1 | >32 | 0.5 | — | |
| 2011 | Erythromycin | 16 | >64 | 33 | 0.03 | 0.125 | 0.5 | >64 | 1 | 0.125 | 0.5 | NT |
| Mupirocin | 0.125 | 2 | 14 | 0.03 | 0.125 | 0.5 | 16 | 1 | 2 | 0.5 | — | |
| 1714 | Retapamulin | 0.03 | 0.25 | 44 | 0.125 | 0.25 | 0.5 | 16 | 2 | 0.25 | 0.5 | — |
| Erythromycin | 8 | 64 | 7 | 0.03 | 0.125 | 0.5 | 16 | 2 | 0.25 | 0.5 | NT | |
| Mupirocin | 0.25 | >32 | 14 | 0.03 | 0.125 | 0.5 | 16 | 2 | >32 | 0.5 | — | |
| 2393 | Erythromycin | 16 | >64 | 33 | 0.03 | 0.125 | 0.5 | 16 | 1 | 0.06 | 0.5 | NT |
| Mupirocin | 0.06 | 1 | 14 | 0.03 | 0.125 | 0.5 | 16 | 2 | 0.5 | 0.5 | — | |
| 2132 | Erythromycin | 0.06 | 0.5 | 24 | 0.03 | 0.125 | 0.5 | 0.5 | 1 | 0.125 | 0.5 | — |
| Mupirocin | 0.06 | 4 | 14 | 0.016 | 0.125 | 0.5 | 0.06 | 0.5 | 4 | 0.5 | — | |
| 2022 | Erythromycin | 0.125 | 1 | 50 | 0.03 | 0.125 | 0.5 | 1 | 2 | 0.125 | 0.5 | NT |
| Mupirocin | 0.25 | >2 | 20 | 0.016 | 0.125 | 0.5 | 0.125 | 1 | 2 | 0.5 | — | |
| 237 | Erythromycin | 1 | 8 | 50 | 0.03 | 0.5 | 0.5 | 8 | 2 | 0.125 | 0.5 | — |
| Mupirocin | 0.25 | 32 | 13 | 0.03 | 0.25 | 1 | 1 | 2 | 16 | 0.5 | — | |
| 2368 | Mupirocin | 0.06 | 1 | 14 | 0.016 | 0.125 | 0.5 | >64 | 1 | 0.5 | 0.5 | — |
| 2620 | Retapamulin | 0.016 | 0.125 | 48 | 0.125 | 0.125 | 0.5 | >64 | 1 | 0.125 | 0.5 | L3 mutation (N149K) |
| Mupirocin | 0.06 | 1 | 14 | 0.016 | 0.125 | 0.5 | >64 | 1 | 0.5 | 0.5 | — | |
a
Quin/Dalfo, quinupristin-dalfopristin.
b
—, mechanism not detected; NT, mechanisms not tested.