# Identification and Genomic Analyses of a Multidrug Resistant Avian Pathogenic Escherichia coli Coharboring mcr-1, blaTEM-176 and blaCTX-M-14 Genes

## TL;DR

This study identifies a multidrug-resistant avian Escherichia coli strain in China that carries genes for colistin resistance and extended-spectrum beta-lactamase, highlighting a public health concern.

## Contribution

The discovery of a coharboring MDR APEC strain with mcr-1, blaTEM-176, and blaCTX-M-14 genes adds new insights into antimicrobial resistance gene dissemination.

## Key findings

- Strain EC012 is resistant to multiple antibiotics including polymyxin B, cefotaxime, and ceftazidime.
- The mcr-1, blaTEM-176, and blaCTX-M-14 genes are located on conjugative plasmids and transferable to other bacteria.
- EC012 belongs to the epidemic APEC serotype O1:H16 and sequence type ST295.

## Abstract

The emergence and transmission of the colistin-resistance gene mcr and extended-spectrum β-lactamase (ESBL) encoding genes pose a significant threat to global public health. In recent years, it has been reported that mcr-1 and ESBL genes can coexist in single bacteria strain. The objective of this study was to characterize a multidrug-resistant (MDR) avian pathogenic Escherichia coli (APEC) isolate carrying mcr and ESBL encoding genes in China. A total of 200 APEC isolates were collected for antimicrobial susceptibility testing by Kirby–Bauer (K–B) disk method. The MDR strain EC012 were then further analyzed for minimum inhibitory concentrations, antimicrobials resistance genes (ARGs) detection, conjugation, and whole-genome sequencing (WGS). Among all APEC isolates determined by K–B disk method, strain EC012 was resistant to almost all the antimicrobials, including polymyxin B, cefotaxime, and ceftazidime. Moreover, EC012 harbored ARGs mcr-1, blaTEM-176, and blaCTX-M-14. WGS analysis revealed that EC012 belonged to epidemic APEC serotype O1:H16 and multilocus sequence type ST295. EC012 consisted of one chromosome and six plasmids, encoding a broad ARGs. The blaCTX-M-14, mcr-1 or blaTEM-176 genes were located on conjugative plasmids pEC012-1 or pEC012-5, respectively. These plasmids were successfully transferred to transconjugants and resulted in the resistance to polymyxin B, cefotaxime, and ceftazidime. This study indicated that APEC was a potential reservoir of colistin-resistance gene mcr-1 and ESBL encoding genes, and highlighted the necessity for enhanced monitoring of ARGs dissemination among bacteria from different origins.