TABLE 3.
Meropenem sensitivity and avibactam potentiation in deletion mutants and transplant derivativesa
| Mutation(s) | No. of isolates tested | Meropenem MIC (μg/mL) |
ΔMIC | |
|---|---|---|---|---|
| –avibactam | +avibactam | |||
| A. baumannii | ||||
| None | 1 | 12 | 0.25 | 48 |
| ΔblaOXA-23 | 2 | 4 | 0.094 | 43 |
| ΔblaGES-14 | 3 | 8 | 0.25 | 32 |
| ΔRI–2 | 1 | 8 | 0.25 | 32 |
| ΔblaOXA-23 ΔblaGES-14 | 3 | 0.094 | 0.094 | 1 |
| ΔblaOXA-23 ΔRI-2 | 1 | 0.094 | 0.094 | 1 |
| A. baylyi | ||||
| None | 1 | 0.064 | 0.031 | 2 |
| + kan | 1 | 0.064 | 0.047 | 1.4 |
| + blaOXA-23 | 2 | 8 | 0.19 | 42 |
| + blaGES-14 | 2 | 0.75 | 0.047 | 16 |
| + blaOXA-23 + blaGES-14 | 2 | 10 | 0.19 | 52 |
MIC values are based on duplicate efficiency of plating assays in LB of independently derived strains. The sample standard deviations were <5% in all cases. The slight (≤2-fold) avibactam potentiation consistently seen for wild-type A. baylyi was eliminated by a mutation inactivating penicillin binding protein 2 (which is not essential in A. baylyi), suggesting that the protein contributes somewhat to the potentiation (not shown). An A. baylyi mutant deleted of lptE reduced the meropenem MIC 12-fold in a bla-minus background and 48-fold in a transplant strain expressing OXA-23 and GES-14, indicating that the lptE-minus sensitivity phenotype is independent of the two β-lactamases. RI-2, resistant island 2 (contains blaGES-14).