Comparative analysis of drug resistance differences and molecular transmission characteristics between animal-derived...

Based on surveillance data from Chinese livestock and poultry farms between 2011 and 2021, we analysed the antimicrobial resistance and transmission characteristics of diarrheagenic Escherichia coli (DEC) and non-diarrheagenic strains.

Phenotypic antibiotic resistance testing, antibiotic resistance gene screening, plasmid typing, and multilocus sequence typing were performed using 1114 identified isolates, and a phylogenetic tree was constructed to assess genetic relationships.

DEC accounted for 2.7% of all strains, with enterotoxin-producing E. coli being the predominant subtype. DEC strains exhibited significantly higher rates of antimicrobial resistance phenotypes, resistance genes, and plasmid carriage than non-DEC strains (P < 0.001), primarily attributable to the host source. Pig-derived DEC strains exhibited significantly higher resistance rates to apramycin, tobramycin, kanamycin, and colistin, as compared with non-DEC strains (P < 0.01), as well as increased carriage rates of mcr-1.1, bla_OXA-1, and aac(3)-IVa and a higher prevalence of IncI and IncHI2. Multilocus sequence typing analysis indicated that DEC strains predominantly comprised ST10 and ST29. The phylogenetic tree revealed that strains clustered according to pathogenicity types; the enterotoxin-producing E. coli branch carried bla_CTX-M-55, consistent with the ceftiofur-resistant phenotype, which was primarily localized to IncF family fusion plasmids.

DEC showed a low prevalence in healthy farmed animals, with the host source having a greater impact on the transmission of antibiotic resistance than the pathogenic type itself. The present findings provide a scientific basis for the rational use of antibiotics and monitoring of antibiotic resistance risks in the Livestock Farming industry.