Plasmid-mediated ciprofloxacin, carbapenem and colistin resistance of a foodborne Escherichia coli isolate

Multidrug resistant (MDR) Escherichia coli poses great threat to human and animal health. To investigate the genetic characteristics of conjugative plasmids that encode ciprofloxacin, carbapenem and colistin resistance in a MDR E. coli strain (974) isolated from pork samples in China, the E. coli strain 974 was subjected to conjugation study, S1-PFGE, Southern hybridization and was sequenced by Illumina Nextseq 500 and MinION Platforms. The ciprofloxacin-resistance-encoding plasmid, p974-IncF, was found to harbor multiple mobile elements that in turn contain genes resistant to β-lactams, quinolone, florephenicol, tetracycline, aminoglycosides, sulfonamides, streptomycin, trimethoprim and chloramphenicol. The backbone of bla_NDM-1-bearing plasmid, p974-NDM, was found consist of a 17.3kb resistance region and a 56.7kb of transfer region. However, the classical ISCR1 mobile element and class I integron were missing in plasmid p974-NDM. Resembling the backbone of other IncI2 plasmids, the mcr-1-bearing plasmid, p974-MCR, contained genes that encode replication function, plasmid stability, proteins related to type IV secretion complex, as well as two pilus-encoding genes, which are conserved among all IncI2 plasmids. Enhanced surveillance efforts and limitation of usage of antibiotics are urgently warranted to control the dissemination of these resistance determinants.