ColE-type plasmid bearing blaOXA-232 increases persister cell formation

Abstract

ObjectivesBacterial persister cells are a sub-population of cells that are tolerant to high concentrations of antibiotics. In this study, we investigated the effect of plasmids bearing carbapenemase genes on persister cell formation. MethodsThree plasmids, IncX3-type plasmid with blaNDM-1, IncN-type plasmid with blaKPC-2, and ColE-type plasmid with blaOXA-232, were transformed into Escherichia coli MG1655. For the ColE-type plasmid (pM5_OXA232), gene-deletion plasmids were constructed and transformed into the MG1655. Persister assays were performed against ciprofloxacin and amikacin, and expression levels of relA and spoT were measured for the wild-type E. coli and all transformants. ResultsUnlike the other two plasmids, transformation of ColE-type plasmid (pM5_OXA232) caused a significant increase in the formation of persister cells. Compared with transformants that harboured intact pM5_OXA232, transformants that harboured plasmids with deletions of gene(s), vbhA, hypothetical gene, or a mobile gene cassette showed decreased persister cell formation. Expression levels of relA and spoT exhibited patterns similar to those of persister cell formation rates, particularly against ciprofloxacin. ConclusionIn this study, we showed that a small ColE-type plasmid bearing blaOXA-232 has an effect on persister cell formation, possibly contributing to the dissemination of low-level carbapanemase.