An insight into analysis and elimination of plasmids encoding metallo-β-lactamases in Pseudomonas aeruginosa

The aim of this study was to characterise metallo-β-lactamase (MBL)-harbouring plasmids, their change in copy number in respect to different antibiotic pressure, and the efficiency of different curing agents in eliminating these resistance plasmids from nosocomial Pseudomonas aeruginosa isolates.

Plasmids were extracted from four isolates harbouring bla_NDM-1 or bla_VIM-2 under four different concentrations of imipenem, meropenem, ertapenem, aztreonam and cefotaxime. Quantitative real-time PCR was performed to analyse the change in plasmid copy number under these different conditions. The effect of different physical and chemical curing agents in elimination of plasmids carrying bla_NDM-1 and bla_VIM-2 was examined, with meropenem resistance used as a selectable marker.

Conjugatively transferable MBL genes (bla_NDM-1 and bla_VIM-2) carried on plasmids were found to be highly stable. Sodium dodecyl sulfate (SDS) was the most effective agent in eliminating these resistance plasmids. The change in copy number of the bla_NDM-1-encoding plasmid was found to be similar to the bla_VIM-2-encoding plasmid, with a single exception under cefotaxime pressure.

The spread of multidrug resistance plasmids has been noted as a key factor associated with increasing carbapenem resistance. Successful curing of resistance plasmids can reverse the bacterial phenotype back to susceptible. This study revealed that different antibiotic pressure induces a change in copy number of MBL-encoding plasmids. SDS can be successfully used as an eliminating agent for these resistance determinants, although therapeutic application of this agent is not possible due to its high toxicity and mutagenic nature.