TABLE 3.

Effect of integron promoter sequences on the relative amounts of blaGES-1 transcripts, β-lactamase activities, and β-lactam resistance levels in E. coli MC4100 strains carrying a plasmid-borne blaGES-1 gene cassette

PromoterSequence at hexamerRelative amt of blaGES-1 transcriptbHydrolysis of nitrocefin (U)cEtest MIC (μg/ml) of β-lactama
−35−10AmxPipCecCxmCazAtmFep
Pc weakTGGACATAAGCT132>2562680.750.0470.032
Pc strongTTGACATAAACT17.0838>25624256>256120.190.19
Pc hybrid 1TGGACATAAACT1.9107>25648321.50.0470.064
Pc hybrid 2TTGACATAAGCT4.6225>256122412840.0940.125
Pc weak+P2TTGTTATACAGT4.7198>25612249640.0940.094
Pc strong+P220.51,030>25624256>256160.250.19
Pc hybrid 1+P26.7365>256162425660.1250.125
ControldNot detectable<1411.520.0640.0320.032
  • a Amx, amoxicillin; Pip, piperacillin; Cec, cefaclor; Cxm, cefuroxime; Caz, ceftazidime; Atm, aztreonam; Fep, cefepime.

  • b Values are the means of three measurements differing by <25% and expressed as relative to that of the Pc weak promoter, set to 1.

  • c Values are the means of three measurements differing by <10%.

  • d Values are from E. coli MC4100 containing a promoterless blaGES-1-carrying integron sequence.