TABLE 1.
Susceptibility data for ceftolozane-tazobactam and β-lactam comparators in a collection of 58 nonfermenting Gram-negative bacilli isolated from cystic fibrosis patients
| Species and antimicrobial agent(s) | MIC (μg/ml) |
EUCAST clinical breakpoint (μg/ml) | No. of strains |
Proportion of susceptible strains (%) | ||||
|---|---|---|---|---|---|---|---|---|
| MIC range | MIC50 | MIC90 | Resistant | Intermediate | Susceptible | |||
| All isolates (n = 58) | ||||||||
| Ceftolozane | 0.5 to >128 | 16 | >128 | |||||
| Ceftolozane + tazobactam | 0.5 to >128 | 16 | >128 | |||||
| Ceftazidime | 4 to >128 | 128 | >128 | |||||
| Piperacillin + tazobactam | 1 to >128 | 64 | >128 | |||||
| Meropenem | 0.5 to >128 | 32 | >128 | |||||
| Pseudomonas aeruginosa (n = 35) | ||||||||
| Ceftolozane | 0.5 to >128 | 4 | 128 | |||||
| Ceftolozane + tazobactama | 0.5 to >128 | 4 | 128 | ≤4 to >4 | 16 | 19 | 54 | |
| Ceftazidime | 4 to >128 | 128 | >128 | ≤8 to >8 | 31 | 4 | 11 | |
| Piperacillin + tazobactam | 2 to >128 | 128 | >128 | ≤16 to >16 | 26 | 9 | 26 | |
| Meropenem | 1 to >128 | 16 | 128 | ≤2 to >8 | 26 | 6 | 3 | 9 |
| Stenotrophomonas maltophilia (n = 12) | ||||||||
| Ceftolozane | 16 to >128 | 64 | >128 | |||||
| Ceftolozane + tazobactam | 16 to >128 | 64 | >128 | ≤4 to >4 | 12 | 0 | 0 | |
| Ceftazidime | 16 to >128 | 128 | >128 | ≤8 to >16 | 11 | 1 | 0 | 0 |
| Piperacillin + tazobactam | 8 to >128 | 128 | >128 | ≤4 to >16 | 11 | 0 | 1 | 8 |
| Meropenem | 4 to >128 | >128 | >128 | ≤2 to >8 | 10 | 2 | 0 | 0 |
| Achromobacter xylosoxydans (n = 11) | ||||||||
| Ceftolozane | >128 | >128 | >128 | |||||
| Ceftolozane + tazobactam | >128 | >128 | >128 | ≤4 to >4 | 11 | 0 | 0 | |
| Ceftazidime | 32 to >128 | >128 | >128 | ≤4 to >8 | 11 | 0 | 0 | 0 |
| Piperacillin + tazobactam | 1 to 64 | 16 | 32 | ≤4 to >16 | 3 | 6 | 2 | 18 |
| Meropenem | 0.5 to >128 | 32 | 128 | ≤2 to >8 | 9 | 1 | 1 | 9 |
a
When CLSI clinical breakpoints were applied, the numbers of P. aeruginosa isolates resistant, intermediate, and susceptible to ceftolozane-tazobactam were 8, 8, and 19, respectively. The proportion of susceptible strains remained unchanged (54%).