TABLE 2.
Mechanisms of resistance to β-lactams detected in the bacteremic P. aeruginosa isolates (n = 69)
| Strain(s) and resistance mechanism(s)a | No. of isolates (no. oprD negative) | Modal MICb (μg/ml)
|
|||||
|---|---|---|---|---|---|---|---|
| FEP | CAZ | ATM | TIC | TZP | IPMc | ||
| Wild-type reference strain PAO1 | 1 | 1 | 4 | 16 | 2 | 1 | |
| Wild-type bacteremic isolates | 39 | 2 | 1 | 4 | 16 | 4 | 1 |
| Resistant bacteremic isolates | |||||||
| XY+ | 19 (4) | 4 | 2 | 4 | 16 | 4 | 8 |
| AmpC+, XY+ | 11 (5) | 16 | 8 | 16 | 128 | 64 | 16 |
| OprD− | 8 (8) | 4 | 2 | 4 | 16 | 4 | 8 |
| AmpC+ | 7 (2) | 8 | 16 | 16 | 64 | 32 | 8-64 |
| PSE-1, XY+ | 5 (1) | 16 | 2 | 8 | >256 | 64 | 64 |
| AmpC+, XY+, PSE-1 | 1 (0) | 16 | 8 | 16 | >256 | 128 | |
| PSE-1 | 2 (0) | 16 | 2-4 | 8-16 | >256 | 128-256 | |
| AmpC+, AB+ | 2 (1) | 8 | 4 | 32 | 128 | 16 | 8 |
| AB+ | 6 (0) | 8 | 4 | 16 | 128 | 16 | |
| AB+, XY+ | 4 (0) | 8 | 2 | 16 | 128 | 8 | |
| AmpC+, XY+, TEM-2 | 1 (0) | 16 | 32 | 16 | >256 | 64 | |
| OXA-2 | 1 (0) | 2 | 2 | 16 | 128 | 8 | |
| AmpC+, AB+, XY+ | 1 (0) | 8 | 16 | 16 | 128 | 64 | |
| XY+, TEM-2 | 1 (0) | 16 | 8 | 8 | >256 | 64 | |
a
Overproduction of MexXY-OprM (XY+) or MexAB-OprM (AB+) pump; production of PSE-1, TEM-2, or OXA-2 β-lactamase; stable overexpression of cephalosporinase AmpC (AmpC+), and deficiency in OprD (OprD−).
b
MICs in the intermediate or resistant categories, according to CLSI breakpoints, are in boldface. FEP, cefepime; CAZ, ceftazidime; ATM, aztreonam; TIC, ticarcillin; TZP, tazocillin/piperacillin; IPM, imipenem.
c
MICs of imipenem are only given for OprD− isolates.