TABLE 1.
Overview of in vitro susceptibility testing for pharyngeal isolates of group A streptococci from nine sites across the United States
| Drug or GAS isolate group | MIC range (μg/ml) | MIC50 (μg/ml) | MIC90 (μg/ml) | No. (%) of nonsusceptible isolatesa | No. (%) of resistant isolatesb |
|---|---|---|---|---|---|
| Erythromycin | |||||
| All isolates (n = 2,797) | 0.06->128.0 | 0.06 | 0.06 | 169 (6.0) | 169 (6.0) |
| M phenotype (n = 115) | 1.00-32.0 | 16.00 | 32.00 | 115 (4.1) | 115 (4.1) |
| MLSi (n = 45) | 2.00->128 | 4.00 | >128.00 | 45 (1.6) | 45 (1.6) |
| MLSc (n = 9) | >128.0 | >128.0 | >128.00 | 9 (0.3) | 9 (0.3) |
| Quinolone | |||||
| All isolates (n = 2,797) | |||||
| Levofloxacin | 0.25-16.0 | 0.50 | 1.00 | 12 (0.43) | 10 (0.36) |
| Gatifloxacin | 0.06-4.0 | 0.25 | 0.50 | 12 (0.43) | 4 (0.14) |
| Telithromycin | |||||
| All isolates (n = 2,797) | 0.015-32.0 | 0.03 | 0.06 | 46 (1.6) | 6 (0.2) |
| Erythromycin-resistant isolates (n = 169) | 0.03-32.0 | 0.50 | 1.00 | 46 (27.2) | 6 (3.6) |
| M phenotype (n = 115) | 0.25-1.0 | 0.50 | 1.00 | 35 (30.4) | 0 (0.0) |
| MLSi (n = 45) | 0.03-8.0 | 0.03 | 0.06 | 2 (4.4) | 2 (4.4) |
| MLSc (n = 9) | 1.0-32.0 | 3.00 | 8.00 | 9 (100) | 4 (44.4) |
a
Nonsusceptible, MIC of ≥0.5, 4.0, 2.0, and 1.0 for erythromycin, levofloxacin, gatifloxacin and telithromycin, respectively.
b
Resistance, MIC of ≥1.0, 8.0, 4.0, and 4.0 for erythromycin, levofloxacin, gatifloxacin, and telithromycin, respectively.