J Hazard Mater. 2026 Jun 27;514:142819. doi: 10.1016/j.jhazmat.2026.142819. Online ahead of print.
ABSTRACT
Dairy farm waste may serve as a reservoir for multidrug-resistant (MDR) Escherichia coli clones, but the genomic characteristics and dissemination potential of such clones remain incompletely understood. Here, we performed whole-genome sequencing and comprehensive genomic analysis of 64 MDR E. coli strains isolated from feces and sewage samples collected from two large dairy farms in Gansu Province, China. Genomic analysis revealed that strains carried 16-32 antibiotic resistance genes (ARGs), 1-6 plasmid replicon types, and 26-96 virulence genes (VGs), with numerically higher (though not statistically significant) counts in feces compared to sewage isolates. Multi-locus sequence typing (MLST) identified globally disseminated clones (ST10, ST38, ST58, ST155) and, for the first time in China, documented the presence of ST1508 (the predominant clone, 42% of isolates), as well as ST2520, ST7207, and ST7588 from dairy farm waste. Network analysis showed co-occurrence of these clones with transferable IncF plasmids harboring broad-spectrum resistance genes (e.g., rmtB, blaCTX-M-55) and multidrug efflux systems (e.g., acrAB-tolC). Contig-level analysis suggested that tet(A) and aph(3′)-IIa were located on IncX1 plasmids, blaTEM-1B on IncFIC(FII), and blaCTX-M-55 on IncI1 plasmids, indicating potential for horizontal gene transfer. These findings identify dairy farm waste as a potential environmental reservoir of MDR E. coli clones with genomic features associated with resistance and virulence. While functional validation of transferability and environmental persistence is needed, the presence of these clones – particularly the emerging ST1508 lineage in untreated farm waste suggests that improved waste management, enhanced surveillance, and integrated One Health strategies may help mitigate dissemination risks. Further studies incorporating environmental sampling, persistence assays, and conjugation experiments are required to establish the actual hazard status.
PMID:42378761 | DOI:10.1016/j.jhazmat.2026.142819
