Abstract
Present study characterized five Escherichia coli co-expressing ESBL and MCR-1 recovered from food, food-producing animals, and companion animals in China. Antimicrobial susceptibility tests, conjugation experiments, and plasmid typing were performed. Whole genome sequencing (WGS) was undertaken for all five isolates using either PacBio RS II or Illumina HiSeq 2500 platforms. The cefotaxime and colistin resistance encoded by blaCTX–M and mcr-1 genes, respectively, was transferable by conjugation either together or separately for all five strains. Interestingly, the ESBL and mcr-1 genes could be co-selected by cefotaxime, while the colistin only selected the mcr-1-carrying plasmids during the conjugation experiments. Five E. coli sequence types (ST88, ST93, ST602, ST162, and ST457) were detected. Although diverse plasmid profiles were identified, IncI2, IncFIB, and IncFII plasmid types were predominant. These five clonally unrelated isolates harbored the mcr-1 gene located on similar plasmid backbones, which showed high nucleotide similarity to plasmid pHNSHP45. The mcr-1 gene can be co-transmitted with blaCTX–M genes through IncI2 plasmids with or without ISApl1 in our study. Characterization of these co-existence ESBL and mcr-1 isolates extends our understanding on the dissemination of these resistance markers among bacteria of diverse origins.
Highlights
Multidrug resistant (MDR) Enterobacteriaceae isolates have been widely reported in non-clinical environments, from pets and farm animals as well as food, which increases the risk for humans regarding the foodborne or zoonotic transmission routes
We reported the characterization of five E. coli isolates, with the aims of this study being (i) to determine the co-occurrence of ESBL and MCR-1 markers, (ii) to identify the co-transference mechanisms by dual conjugation assays, (iii) to characterize the E. coli by Whole genome sequencing (WGS), and (iv) to identify the plasmid backbones and genetic environments containing the mcr-1 genes
The cefotaxime resistance determinant was confirmed as blaCTX−M−55 by PCR in CQ9-C-(T) and CQ9-M-(T) and as blaCTX−M−64 in F89C-(T) and F89-M-(T), which showed the donor strains of the two had the mcr-1 gene and blaCTX−M gene co-transferred on the same plasmid (Figure 1)
Summary
Multidrug resistant (MDR) Enterobacteriaceae isolates have been widely reported in non-clinical environments, from pets and farm animals as well as food, which increases the risk for humans regarding the foodborne or zoonotic transmission routes. Various plasmid replicon types, such as IncI2, IncHI1, IncHI2, IncP, IncFIB and IncX4 have been reported to be associated with HGT of the mcr genes (Doumith et al, 2016; Poirel et al, 2016; Zurfluh et al, 2016). It is unusual, but not without precedent, that mcr-1 has already been found to coexist with both ESBL and blaNDM−1 (or its variants blaNDM−5 and blaNDM−9) on these promiscuous plasmids (Du et al, 2016; Haenni et al, 2016; Li Y. et al, 2018). We reported the characterization of five E. coli isolates, with the aims of this study being (i) to determine the co-occurrence of ESBL and MCR-1 markers, (ii) to identify the co-transference mechanisms by dual conjugation assays, (iii) to characterize the E. coli by WGS, and (iv) to identify the plasmid backbones and genetic environments containing the mcr-1 genes
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