Table 3.

β-lactam susceptibility of E. coli strains expressing components of the P. aeruginosa multidrug efflux pumpsa

PlasmidEfflux genesMIC (μg/ml)b,c
pRK415d 163240.1280.064
pRSP17 mexAB-oprM 128128320.5120.128
pRSP15 mexCD-oprJ 323240.2560.064
pRSP25 mexCD 323240.2560.064
  • a The susceptibility of E. coli KZM120 (ΔacrAB::kan) carryingP. aeruginosa multidrug efflux genes on the indicated plasmids to various antimicrobial agents was assayed as described in Materials and Methods.

  • b AMP, ampicillin; PEN, penicillin G; TIC, ticarcillin; CPZ, cefoperazone; TAX, cefotaxime.

  • c E. coli KZM120 carrying pRSP08 (oprM), pRSP19 (mexAB) and pRSP06 (oprJ) showed the same resistance pattern as that exhibited by KZM120 carrying pRK415. β-lactams for which no change in susceptibility was observed for KZM120 with or without plasmids containing efflux genes included cephaloridine, cefsulodin, cefepime, cefpirome, imipenem, ceftriaxone, and ceftazidime.

  • d —, no plasmid-borne efflux genes.