Genomic characterization of carbapenem resistant Escherichia coli from multiple hospitals in Nanjing, China: focusing on frequent co-occurrence of blaNDM and blaKPC-2 

Abstract Background: The increasing emergence of carbapenem resistant Escherichia coli (CREC) poses a potential threat to public health, hence genomic characterization of isolates is needed for a better understanding of its transmission and implementation of infection control measures. Materials and methods：Eleven CREC isolates were collected in 2015 from 6 hospitals in Nanjing, China, and analyzed using whole genome sequencing. Resistance determinants, virulence elements, multi-locus sequence type (MLST), serotypes, phylogeny and fimH types were determined. Results: All of the CREC carried at least one carbapenemase. NDM-5 (n=9) was the most frequent carbapenemase, followed by KPC-2 (n=3) and NDM-1 (n=2); three isolates produced NDM-5 and KPC-2. Ten out of the 11 isolates co-carried blaCTX-M variants. MLST analysis found 7 distinct STs, including ST410 (n=2), ST3489 (n=1), ST156 (n=1), ST683 (n=1), ST297 (n=1), ST167 (n=1), and ST361 (n=1). Six distinct serotypes and 8 Fim types were identified. A great diversity of plasmid profiles was observed with plasmid replicon IncX3 being the most frequent (n=11). Phylogenetic analysis showed great diversity between the 11 CREC isolates and also between 6 additional isolates co-carrying blaNDM and blaKPC which were selected from the strains collection of Nanjing Drum Tower Hospital for comparison. Conjugation assays demonstrated that blaNDM was transferable. Conclusion: NDM is the major carbapenemase among CREC, with NDM-5 being the main variant which can be horizontally disseminated by IncX3 plasmids. These isolates displayed genetic diversity by MLST, Fim typing and serotyping. We herein provided the first report on emergence of NDM-5 producing E. coli ST297, ST683, ST3489, and NDM-1 producing E. coli ST361.