Genetic Characterization of Colistin-Resistant ST34 Co-Harbouring Plasmid-Borne and Recovered from a Paediatric Patient in Shenzhen, China.

Background: Since 2015, plasmid-borne has been reported in various bacterial strains in the clinical setting globally. However, the transmission mechanisms of this gene in are not well defined. This study aimed to characterize the genomic features of a ST34 isolate, which carried a , mapped to a carbapenemase and extended spectrum β-lactamase encoding gene located on the IncX4 plasmid.

Methods: was recovered from a diarrheal paediatric patient in Shenzhen, China. Antimicrobial susceptibility testing was performed by using the VITEK 2 system. Drug resistance genes were identified using targeted primers and Sanger sequencing. The transferability and genome location of was determined by performing conjugation, S1-PFGE and Southern blot hybridization analysis. WGS was performed by Illumina MiSeq sequencing and was assembled using the A5-Miseq pipeline, and gene annotation was performed using RAST 2.0. The database Centre for Genomic Epidemiology's website was used to identify resistance genes and sequence types (STs).

Results: We found that the isolate was extensively drug resistant and belonging to ST34, carrying an IncX4 plasmid with and We also noticed that genes , , the mutation in and (MexEF-OprN efflux regulator), and exotoxin-encoding genes ( and ) were associated with resistance and virulence in the genome. In addition, heavy metal resistance genes as were determined.

Conclusion: This study highlights the potential risk of ST34 of serotype Typhimurium carrying multiple drug resistance encoding genes in a single IncX4 plasmid.