Research note: Emergence of blaNDM-13 producing Escherichia coli from a broiler chicken and farm environment in Jiangsu Province, China.

Carbapenem-resistant bacteria, in particular NDM-producing Enterobacteriaceae, have become a great threat to the global public. The blaNDM-13 is a novel blaNDM variant with increasing dydrolytic activity against cefotaxime. This study aimed to investigate the molecular characteristics of blaNDM-13-positive E. coli in a chicken farm located in Jiangsu Province of China. Six blaNDM-13-positive E. coli strains were isolated from 83 samples, including cloacal samples (n = 4), cages (n = 1), and water dispensers (n = 1). Antimicrobial susceptibility testing showed that these isolates exhibited pan-resistance to β-lactams (meropenem MIC≥32 μg/mL), colistin, and six other antibiotic classes, retaining susceptibility only to tigecycline. Illumina sequencing showed that isolates harbored multiple resistance genes, with fosA3, aph(3')-IIa, oqxA, oqxB, and aph(6)-Id being present in all strains. Notably, blaCTX-M-65 (extended-spectrum β-lactamase), mcr-1.1 (colistin resistance), and qacE (disinfectant genes) were detected in 50 %, 66.67 %, and 66.67 % of blaNDM-13-positive E. coli strains, respectively. MLST classified the isolates into ST155 (n = 3), ST93 (n = 2), and ST1158 (n = 1), with blaNDM-13-positive ST155 E. coli isolates found to be horizontal transmission between chicken and environmental surface samples. Three representative isolates were subjected to Nanopore long-read sequencing; the blaNDM-13 was located on the IncFII plasmid, which showed high homology with clinical (pB5-1) and poultry-derived plasmids (YZLc23-1-NDM-13-96k), harboring conserved resistance gene clusters (IS91-blaNDM-13-bleMBL-IS50R-aph(3')-IIa-IS26-IS6-fosA3), and confirmed horizontal transfer via conjugation. The conjugants were stably inherited after 15 days of passage and exhibited no significant differences in growth rates when compared to E. coli J53. This study identifies blaNDM-13-carrying multidrug-resistant E. coli clones in poultry production systems, transmitted via poultry-environment interactions and plasmid-mediated gene transfer. Farm-level surveillance targeting high-risk transmission routes is essential to control antimicrobial resistance and protect poultry health.