TABLE 3.
Distribution of MICs for ceftolozane-tazobactam against E. coli isolates with blaCTX-M genes
| Antibiotic used | Enzyme type (n) | Testing method | No. (cumulative %) of isolates with MIC (μg/ml) of: |
MIC (μg/ml) |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ≤0.25 | 0.5 | 1 or ≤1 | 2 | 4 | 8 | 16 | 32 | 64 | >64 | MIC50 | MIC90 | |||
| Ceftolozanea | CTX-M-14 (26) | BMD | 1 (4) | 3 (15) | 13 (65) | 7 (92) | 1 (96) | 1 (100) | 4 | 8 | ||||
| Ceftolozane-tazobactamb | CTX-M-14 | BMD | 20 (77) | 4 (92) | 2 (100) | ≤0.25 | 0.5 | |||||||
| Ceftolozane-tazobactam | CTX-M-14 | Etest | 22 (85) | 3 (96) | 1 (100) | ≤0.25 | 0.5 | |||||||
| Ceftolozane | CTX-M-15 (219) | BMD | 2 (1) | 1 (1) | 2 (2) | 5 (5) | 31 (19) | 67 (49) | 52 (73) | 59 (100) | 64 | >64 | ||
| Ceftolozane-tazobactam | CTX-M-15 | BMD | 161 (74) | 45 (94) | 13 (100) | ≤0.25 | 0.5 | |||||||
| Ceftolozane-tazobactam | CTX-M-15 | Etest | 170 (78) | 37 (95) | 11 (99.5) | 1 (100)c | ≤0.25 | 0.5 | ||||||
a
Ceftolozane was tested at ≥1 μg/ml and was tested for MICs by BMD only.
b
Tazobactam was tested at a concentration of 4 μg/ml.
c
MIC was recorded as 1.5 μg/ml in duplicate readings.