FIG 2.

Plasmid multimerization enhances carbapenem resistance. (A) Copy numbers of bla_IMP-6 per cell of E. coli transformants JW188, ME188, JW044, and ME044. Copy numbers of bla_IMP-6 in transformant cells were determined by qPCR, using rrsA as an internal control gene. Bars indicate the mean ± standard deviation, calculated from quadruple experiments. WT; wild type. (B) MICs of meropenem (MEPM) for E. coli transformants. Points indicate the results of triplicate experiments. (C) Transcript levels of bla_IMP-6 in E. coli transformants. bla_IMP-6 transcription in transformant cells was measured by reverse transcription (RT)-qPCR. The bar chart represents the relative mRNA transcript ratio of bla_IMP-6 to that of rrsA. Bars indicate the mean ± standard deviation calculated from quintuple experiments. (D) Increased bla_IMP-6 copy numbers in ME044 cells after overnight exposure to meropenem. Copy numbers of bla_IMP-6 in transformant cells were determined by qPCR, using rrsA as an internal control. Bars indicate the mean ± standard deviation, calculated from nonuple experiments. (E) The MIC of meropenem for transformant ME044 is increased after preexposure (overnight) to meropenem. MICs were measured by modified methods (see Text S1 in the supplemental material). The bars indicate medians ± standard deviation calculated from nonuple experiments. Statistical analysis was performed using Mann-Whitney U tests; *, P < 0.05; ns, not significant.