TABLE 2.

MICs for ampD clones in WT and ampD mutant E. coli background

Plasmid or origin of ampD insertampD insert characteristic(s)K-12 259a,kJRG582b,k
CAZ MICc (μg/ml)Zone diamd (mm)CAZ MICc (μg/ml)Zone diamd (mm)
Plasmids
    NoneNo ampD insert0.25 (S)30 (S)0.064 (S)32 (S)
    ACYC184 (ampR blaACT-1)No ampD insert12 (S)19 (S)>256 (R)6 (R)
Origin of ampD insert
    E. coli
        HB101eWT16 (I)19 (S)24 (I)18 (S)
        CUMC5fV9A, C143R, K149N, 176A, V178I16 (I)19 (S)12 (S)19 (S)
    C. freundii
        CF21gR175S16 (I)19 (S)4 (S)19 (S)
        CF21MhR175S24 (I)19 (S)12 (S)19 (S)
        CF21-XIR1TAG at E16024 (I)17 (I)>256 (R)6 (R)
        CF21-XIR2TAG at P16524 (I)18 (S)>256 (R)6 (R)
        CF21-XIR3TAG at R175S16 (I)19 (S)>256 (R)8 (R)
    P. aeruginosa
        PAO1WT16 (I)19 (S)24 (I)18 (S)
        Ps164iWT24 (I)19 (S)32 (R)16 (I)
        Ps164 M1jTAG at Q15516 (I)16 (I)>256 (R)6 (R)
  • a E. coli strain K-12 259: WT ampD.

  • b JRG582: E. coli strain K-12 derivative lacking the ampD gene(23).

  • c Ceftazidime MICs were determined using Etest strips, and susceptibility breakpoints reflect those indicated by CLSI guidelines (29).

  • d Disk diffusion tests for ceftazidime, 30 μg.

  • e E. coli strain HB101 is a laboratory control strain with wild-type β-lactam susceptibility patterns.

  • f E. coli strain CUMC5 is a urine isolate.

  • g C. freundii strain CF21 is a clinical isolate which has an inducible chromosomal ampC (38).

  • h C. freundii strain CF21M is a derepressed (noninducible) mutant derived from CF21 (38).

  • i P. aeruginosa strain Ps164 is a clinical isolate susceptible to all β-lactam drugs (10).

  • j P. aeruginosa strain Ps164 M1 is a partially derepressed mutant selected from Ps164 using cefotaxime (10).

  • k S, susceptible; I, intermediate; R, resistant.