TABLE 1

MICs, β-lactamase activities, and ampC expression levels of CFE-1 β-lactamase-producing E. coli isolates and their reconstructed transformants

StrainGenotypeAmpR
characteristic
MIC (μg/ml)aβ-Lactamase
activity (U/mg
of protein)b
ampC mRNA
expressionc
AMPCEFCPDCTXCMZ
E. coli(pKU601) ampC ampR AmpR135A>256>256>2561281282.971.0
E. coli(pKU602) ampC ampR::Kmr32256322160.100.17
E. coli(pAmpR135
A, pKU602)
ampC ampR AmpR135A>256>256128641282.170.82
E. coli(pAmpR135
D, pKU602)
ampC ampR AmpR135D86440.580.020.06
E. coli 120.25<0.060.25<0.01NDd
  • a Antibiotics: AMP, ampicillin; CEF, cephalothin; CPD, cefpodoxime; CTX, cefotaxime; CMZ, cefmetazole.

  • b β-Lactamase activities are the geometric mean values of three independent cultures. The standard deviations were within 10%.

  • c Values are relative to the expression of E. coli(pKU601), which was assigned a value of 1. The standard deviations were within 10%.

  • d ND, not done.