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

Abstract

Objectives: Bacterial 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.

Methods: Three plasmids, IncX3-type plasmid with bla_NDM-1, IncN-type plasmid with bla_KPC-2, and ColE-type plasmid with bla_OXA-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.

Results: Unlike 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.

Conclusion: In this study, we showed that a small ColE-type plasmid bearing bla_OXA-232 has an effect on persister cell formation, possibly contributing to the dissemination of low-level carbapanemase.

Keywords: Antitoxin; Carbapenemase; Persister; Plasmid.