NDM-5-Producing Escherichia coli Co-Harboring mcr-1 Gene in Companion Animals in China

Simple Summary This is a study related to NDM-5-producing E. coli in companion animals in China. Notably, an E. coli isolate possessing both bla(NDM-5)-bearing plasmid and mcr-1-bearing plasmid was identified in a dog from the same veterinary clinic, where we previously found the mobile IncX3-X4 hybrid plasmid encoding both bla(NDM-5) and mcr-1 in a cat. This observation highlights the diversity of bla(NDM-5)- and mcr-1-harboring plasmids and the transferability of such resistant pathogens from companion animals to humans. Given that colistin is the last-resort antibiotic for treating human infections caused by carbapenem-resistant Enterobacteriaceae, the co-transfer of resistance to both antibiotics may seriously compromise the effectiveness of clinical therapy. Carbapenem and colistin are important antibiotics for the treatment of infections caused by multidrug-resistant Gram-negative pathogens. Here, we isolated the bla(NDM-5)-harboring Escherichia coli in companion animals in healthy or diseased companion animals from veterinary clinics in six cities in China from July to November 2016. A total of 129 rectal swabs of healthy or diseased dogs and cats were collected from veterinary clinics in six different cities in China, and the isolates were subjected to carbapenem and colistin susceptibility testing. Resistance genes were confirmed using PCR. Conjugation experiments were conducted to determine the transferability of antibiotic resistance genes (ARGs) in the strains. The isolated rate of bla(NDM-5)-harboring E. coli strains was 3.88% (five strains). These five strains were multidrug resistant to at least three antibiotics and corresponded to four sequence types including ST101. The bla(NDM-5) gene was located on 46 kb IncX3 plasmids in these five strains, and the genetic contexts were shared and were nearly identical to the K. pneumoniae plasmid pNDM5-IncX3 from China. In addition, one strain (CQ6-1) co-harbored bla(NDM-5)-encoding-IncX3 plasmid along with a mcr-1-encoding-IncX4 plasmid, and their corresponding genetic environments were identical to the bla(NDM-5)-IncX3 and mcr-1-IncX4 hybrid plasmid reported previously from the same area and from the same clinic. The results indicated that the similar genetic contexts were shared between these isolates from companion animals, and the IncX3-type plasmids played a key role in the spread of bla(NDM-5) among these bacteria.