Molecular epidemiology and pathogenic potential of mcr-1-positive Escherichia coli isolated from healthy and diseased poultry in Jiangxi, China

Introduction The emergence and dissemination of mcr-1 has raised global public health concerns, and poultry is a major reservoir. However, systematic investigations of mcr-1 -positive Escherichia coli in Jiangxi Province, an important poultry production base in southern China, remain limited. Methods From 2020 to 2024, 591 E. coli strains were collected from diseased ( n = 291) and healthy ( n = 300) poultry across 11 cities in Jiangxi Province. mcr-1 -positive strains were identified by colony PCR. The minimum inhibitory concentrations were determined for 16 antimicrobial agents. Whole-genome sequencing and bioinformatics analysis were conducted. Pathogenicity was assessed using the Galleria mellonella infection model. Results Among the 591 strains, 24 were mcr-1 -positive, including 15 avian pathogenic E. coli (APEC) strains from diseased poultry and 9 intestinal E. coli strains from healthy poultry. All 24 isolates exhibited colistin resistance and 100% multidrug resistance. High resistance rates were observed for apramycin (100%), sulfisoxazole (100%), ampicillin (95.83%), ceftiofur (95.83%), tetracycline (95.83%), and sulfamethoxazole-trimethoprim (95.83%), whereas all isolates remained susceptible to meropenem. Genomic analysis identified a diverse array of acquired resistance genes, including tet(A) , bla CTX-M , sul2 , and floR , consistent with the phenotypic resistance profile. mcr-1 was predominantly located on IncI2 plasmids, with chromosomal integration detected in eight APEC isolates. Virulence genotypic analysis revealed high prevalence of key APEC-associated genes ( iss , ompT , hlyF, iroN , iutA ), whereas iucD and papG were absent in all isolates. The infection assay demonstrated strong lethality in most isolates, with some intestinal E. coli from healthy poultry also exhibiting high mortality rates. Discussion The coexistence of plasmid-borne and chromosome-integrated mcr-1 genomically suggests dual maintenance mechanisms with potential transmissibility. Intestinal E. coli from healthy poultry carried higher resistance burden and virulence potential, revealing a hidden reservoir. These findings suggest the need for expanded surveillance, prudent antimicrobial use, and functional validation to further assess the potential dual threat to animal and public health.