Characterization of NDM-5-producing isolates from retail grass carp ( ) and evidence of -bearing IncHI2 plasmid transfer between ducks and fish.

We aimed to characterize NDM-5-producing from aquatic products in Guangzhou, China. A total of 196 intestinal samples of grass carp collected in 2019 were screened for carbapenemase genes. Characterization of positive isolates and plasmids was determined by antimicrobial susceptibility testing, conjugation experiments, Illumina HiSeq, and Nanopore sequencing. One and six strains recovered from seven intestinal samples were verified as carriers (3.57%, 7/196). The genes were located on the IncX3 ( =5), IncHI2 ( =1), or IncHI2-IncF ( =1) plasmids. All -bearing plasmids were transferred by conjugation at frequencies of ~10 -10 . Based on sequence analysis, the IncHI2 plasmid pHNBYF33-1 was similar to other -carrying IncHI2 plasmids deposited in GenBank from Guangdong ducks. In all IncHI2 plasmids, was embedded in a novel transposon, Tn (IS -ΔIS -IS -ΔIS - - - - -∆ -IS -∆ -∆IS -IS ), which was identical to the genetic structure surrounding found in some IncX3 plasmids. The IncHI2-IncF hybrid plasmid pHNTH9F11-1 was formed by homologous recombination of the -carrying IncHI2 plasmid and a heavy-metal-resistant IncF plasmid through ∆Tn . To the best of our knowledge, this is the first report on the characterization of -bearing plasmids in fish in China. The IncHI2 plasmid pHNBYF33-1 may be transmitted from ducks, considering the common duck-fish freshwater aquaculture system in Guangdong. Tn is likely responsible for the transfer of from IncX3 to IncHI2 plasmids in , resulting in the expansion of transmission vectors of .