Genomic epidemiology and plasmid characterization of antimicrobial resistance and virulence in cattle <i>Escherichia coli</i> from China

Antimicrobial resistance (AMR) in <i>Escherichia coli</i> from livestock poses a growing public health threat, yet genomic data on cattle-derived strains in China remain limited. This study investigated AMR, virulence, and plasmid profiles of <i>E. coli</i> from diarrheic cattle in four provinces: Anhui (AH), Ningxia (NX), Shandong, and Shanxi (SX). Ninety-one isolates were characterized using antimicrobial susceptibility testing and whole-genome sequencing. Resistance to ampicillin (49.5%), cefotaxime (37.4%), and tetracycline (36.3%) was common, with NX showing the highest resistance rate. Twenty-one multidrug-resistant strains were identified, mainly from NX and SX. Genomic analysis revealed 53 distinct antibiotic resistance genes (ARGs), predominantly <i>mdf</i>(<i>A</i>), <i>aph</i>(6)-<i>Id</i>, and <i>tet</i>(A), with the highest burdens in NX and SX. Among 196 virulence genes, adherence (<i>fim</i> and <i>csg</i>) and secretion systems (<i>espX</i>, <i>espR</i>) predominated, with AH showing the greatest diversity. Plasmid profiling detected 37 replicon types, with incompatibility FIB (IncFIB) being the most abundant. A strong correlation between plasmids and ARGs was found (<i>r</i> = 0.626, <i>P </i>< 0.001), with key ARGs [<i>bla</i>_CTX-M-55, <i>tet</i>(A)] located on IncI1 and IncX1 plasmids, while most virulence genes were chromosomal. Molecular typing identified 45 sequence types (STs) and 59 serotypes, with ST29 (O26:H11) unique to AH and ST1011 (O86:H51) to NX. Phylogenetic analysis revealed clustering by phylogroup, with shared STs and serotypes across regions, indicating clonal and geographic dissemination. These findings underscore the genomic diversity and dissemination risk of AMR <i>E. coli</i> in Chinese cattle, highlighting the need for region-specific surveillance.IMPORTANCEThe growing threat of antimicrobial resistance (AMR) in <i>Escherichia coli</i> from livestock raises serious concerns for both animal and public health, especially under the One Health framework. Genomic information on cattle-derived <i>E. coli</i> in multi-regions of China has been limited, hindering our understanding of regional AMR patterns. This study addresses that gap by analyzing isolates from diarrheic cattle across four provinces, uncovering clear geographic variation in resistance profiles, virulence traits, and plasmid content. The identification of clinically relevant resistance genes such as <i>bla</i>_CTX-M-55 and <i>tet</i>(A) on plasmids indicates a high potential for horizontal gene transfer. The strong association between plasmid types and resistance gene burden highlights key targets for surveillance. These findings offer valuable insights into the molecular epidemiology of bovine <i>E. coli</i> and support more effective, region-specific strategies to monitor and control the spread of AMR in livestock.