TABLE 1.
MIC50/90 and susceptibility percentages for the entire collection of bloodstream isolates and subsets of isolates showing AmpC or efflux pump hyperproduction or MDR profiles
| MIC or susceptibility | All isolates (n = 190) |
AmpC-hyperproducing isolates (n = 46)a |
MexAB-hyperproducing isolates (n = 24)a |
MexXY-hyperproducing isolates (n = 25)a |
MDR isolates (n = 63) |
Pan-β-lactam-resistant isolates (n = 27)b |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CAZ | CAZ-AVI | MER | CAZ | CAZ-AVI | MER | CAZ | CAZ-AVI | MER | CAZ | CAZ-AVI | MER | CAZ | CAZ-AVI | MER | CAZ-AVI | |
| MIC50 (μg/ml) | 4 | 4 | 1 | 32 | 4 | 8 | 8 | 8 | 8 | 8 | 4 | 8 | 32 | 4 | 8 | 8 |
| MIC90 (μg/ml) | 32 | 8 | 16 | 128 | 16 | 32 | 64 | 16 | 32 | 32 | 8 | 16 | 128 | 16 | 32 | 16 |
| % susceptiblec | 64.7 | 91.1 | 77.4 | 10.9 | 76.1 | 41.3 | 50.0 | 87.5 | 41.7 | 60.0 | 96.0 | 44.0 | 27.0 | 77.8 | 41.3 | 74.1 |
Previous definitions were used (5). Strains were considered positive for ampC or mexY overexpression when the corresponding mRNA level was at least 10-fold higher than that of PAO1. Strains were considered positive for mexB overexpression when the corresponding mRNA level was at least 3-fold higher than that of PAO1.
Pan-β-lactam-resistant isolates are defined as nonsusceptible to ceftazidime, cefepime, aztreonam, piperacillin-tazobactam, imipenem, and meropenem.
Breakpoints for ceftazidime (CAZ) susceptibility (S), ≤8 μg/ml; ceftazidime-avibactam (CAZ-AVI) S, ≤8/4 μg/ml; meropenem (MER) S, ≤4 μg/ml.