Occurrence and Characterization of NDM-1-Producing Shewanella spp. and Acinetobacter portensis Co-Harboring tet (X3) in a Chinese Dairy Farm.

Bacteria with carbapenem or tigecycline resistance have been spreading widely among humans, animals and the environment globally, being great threats to public health. However, bacteria co-carrying drug resistance genes of carbapenem and tigecycline in Shewanella and Acinetobacter species remain to be investigated. Here, we detected nine bla NDM-1 -carrying Shewanella spp. isolates as well as three A. portensis isolates co-harboring tet (X3) and bla NDM-1 from seventy-two samples collected from a dairy farm in China. To explore their genomic characteristic and transmission mechanism, we utilized various methods, including PCR, antimicrobial susceptibility testing, conjugation experiment, whole-genome sequencing, circular intermediate identification and bioinformatics analysis. Clonal dissemination was found among three A. portensis , of which tet (X3) and bla NDM-1 were located on a novel non-conjugative plasmid pJNE5-X3_NDM-1 (333,311 bp), and the circular intermediate ΔIS CR2 - tet (X3)- bla NDM-1 was identified. Moreover, there was another copy of tet (X3) on the chromosome of A. portensis . It was verified that bla NDM-1 could be transferred to Escherichia coli C600 from Shewanella spp. by conjugation, and self-transmissible IncA/C 2 plasmids mediated the transmission of bla NDM-1 in Shewanella spp. strains. Stringent surveillance was warranted to curb the transmission of such vital resistance genes.