Multiple Copies of qnrA1 on an IncA/C 2 Plasmid Explain Enhanced Quinolone Resistance in an Escherichia coli Mutant.

In a previous study, mutants with enhanced ciprofloxacin resistance (Cip(r)) were selected from Escherichia coli J53/pMG252 carrying qnrA1. Strain J53 Cip(r) 8-2 showed an increase in the copy number and transcription level of qnrA1. We sequenced the plasmids on Illumina and MinION platforms. Parental plasmid pMG252 and plasmid pMG252A from strain J53 Cipr 8-2 were almost identical, except for the region containing qnrA1 that in pMG252A contained 4 additional copies of the qnrA1-qacE Delta 1-sull-ISCR1 region.