TABLE 4.

Levels of ampC expression under basal and cefoxitin-induced conditions and MICs of antipseudomonal β-lactams for strain PAO1 and seven ampD mutants

StrainAvg level of ampC expressiona ± SDMIC (μg/ml)b
BasalInducedCAZ (≤8->16)FEP (≤8->16)TIC (≤64->64)PIP (≤64->64)PIP-TZ (≤64->64)ATM (≤8->16)IMP (≤4->8)MER (≤4->8)
PAO143 ± 911122411.50.38
PAΔD60 ± 19152 ± 3884326496621
PAΔDh2NCc48 ± 150.75181.53110.38
PAΔDh3NC55 ± 51112341.510.38
PAΔDh2Dh32.3 ± 0.1481 ± 260.7516230.51.50.38
PAΔDDh262 ± 9234 ± 58121225648641610.38
PAΔDDh3191 ± 521,014 ± 2974832>256>256>256161.52
PAΔDDh2Dh31,020 ± 871,105 ± 884832>256>256>256241.52
  • a Relative amount of ampC mRNA compared to PAO1 basal expression. Induction experiments were carried out with 50 μg/ml cefoxitin.

  • b CAZ, ceftazidime; FEP, cefepime; TIC, ticarcillin; PIP, piperacillin; PIP-TZ, piperacillin-tazobactam; ATM, aztreonam; IMP, imipenem; MER, meropenem. CLSI susceptibility and resistance breakpoints for each antibiotic are shown in parentheses (5a).

  • c NC, no change in ampC mRNA level compared to PAO1 basal expression.