Antimicrobial resistance and genomic characterization of Escherichia coli isolated from mink in northern China.

Escherichia coli (E. coli) is one of the most common commensal bacteria in the intestinal tract of humans and animals. It serves as a major reservoir of antimicrobial resistance genes and may facilitate their horizontal transfer among different hosts. In this study, 212 fecal samples were collected from mink across four northern provinces of China, a total of 110 E. coli isolates were recovered (isolation rate, 51.89 %). Preliminary antimicrobial screening was conducted using four clinically critical antibiotics, including ceftazidime (CAZ), polymyxin B (PMB), meropenem (MEM), and tigecycline (TGC), with CAZ resistance being the most prevalent, followed by PMB, MEM, and TGC. Further antimicrobial susceptibility testing against ten commonly used antibiotics in 49 representative isolates revealed universal multidrug resistance (MDR), including 100 % resistance to imipenem, tetracycline, enrofloxacin, florfenicol, and sulfamethoxazole. Genetic screening identified multiple resistance genes such as aac(3')-IIa, blaCTX-M, tet(A), and mcr-1. Conjugation assays demonstrated that CAZ resistance was the most transferable. Virulence profiling revealed a low prevalence of classical pathogenic virulence factors, with only six virulence gene types detected, consistent with the results of Galleria mellonella infection assays. Whole-genome sequencing of 41 representative isolates revealed 87 unique antibiotic resistance genes (ARGs) types spanning 14 antibiotic classes including alinically important determinants such as blaCTX-M, tet, and mcr, and 71 unique virulence genes assigned to 65 functions. Metagenomic analysis further identified diverse ARGs within the mink gut microbiota, with 21 shared between whole-genome and metagenomic sequencing. Correlation analysis suggested co-occurrence patterns among ARGs, virulence factor genes (VFGs), and mobile genetic elements (MGEs), particularly between ARGs and MGEs. Overall, mink-derived E. coli exhibited extensive MDR but limited classical pathogenic virulence, and the mink gut microbiota may represent an important reservoir and transmission hub for resistance genes in intensive farming ecosystems.