Identification and Characterization of Antibiotic Resistance Genes from a Multi-drug Resistant Escherichia coli C20 Isolated from Guts of Chicken

Spreading of antibiotic resistant bacteria in the environment has become a major concern for food safety and human health. Escherichia coli C20 was isolated from the gut microbiota of a domestic chicken that showed resistances to 7 out of 10 tested antibiotics. To elucidate the underlying mechanism, origin, and transmission of the resistances, published information on C20 genome were reviewed for a detailed analysis. There were 80 antibiotic resistance determinants, including the abovementioned 7 drugs, annotated in E. coli C20 genome from the databases. Among them, the fluoroquinolone-resistant genes were identified in the chromosomes, while those resistant to tetracycline, sulphonamide, chloramphenicol, and aminoglycoside found to be expressed in the plasmids of C20. A phylogenomic analysis on C20 revealed a clustering of the strain with E. coli K-12 group, especially the substrains of DH1, BW2952 and MG1655. Their genomic nucleoid sequences shared 97-99% homology. There was no plasmid pC20-like sequence found in the genomic sequences of 3 K-12 strains reported previously. It was proposed that E. coli C20 isolated from the chicken guts might have acquired the antibiotic resistance through plasmid transfer from environmental microbiome.