Epidemiological characteristics of human- and chicken-derived CTX-M-type extended-spectrum β-lactamase-producing...

Bacterial resistance to β-lactams is mainly attributed to CTX-M-type extended-spectrum β-lactamases (ESBLs). However, the predominant sequence type (ST) of bla_CTX-M-carrying Escherichia coli (bla_CTX-M-Ec) in chickens, an important food animal, in China and its contribution to human β-lactam resistance are not investigated. In this study, approximately 1808 chicken-derived strains collected from 10 provinces from 2012 to 2020 were screened for bla_CTX-M-Ec, and 222 bla_CTX-M-Ec were identified. Antimicrobial susceptibility tests, whole genome sequencing and conjugation experiment were performed. All quality-controlled 136 chicken-derived bla_CTX-M-Ec and 1193 human-derived bla_CTX-M-Ec genomes were downloaded from NCBI and EnteroBase to comprehensively analyze the prevalence of bla_CTX-M-Ec in China. bla_CTX-M-55 (153/358, 42.7% in chicken isolates; 312/1193, 26.2% in human isolates) and bla_CTX-M-14 (92/358, 25.7% in chicken isolates; 450/1193, 37.7% in human isolates) were dominant in bla_CTX-M-Ec. The STs of bla_CTX-M-Ec were diverse and scattered, with ST155 (n = 21) and ST152 (n = 120) being the most abundant in chicken- and human-derived isolates, respectively. Few examples indicated that chicken- and human-derived bla_CTX-M-Ec have 10 or less core genome single nucleotide polymorphisms (cgSNPs). Genetic environment analysis indicated that ISEcp1, IS26 and IS903B were closely associated with bla_CTX-M transfer. The almost identical pc61-55 and pM-64-1161 indicated the possibility of plasmid-mediated transmission of bla_CTX-M between humans and chickens. Although the genomes of most bla_CTX-M-Ec isolated from chickens and humans were quite different, the prevalence and genetic environment of bla_CTX-M variants in both hosts were convergent. CTX-M-mediated resistance is more likely to spread through horizontal gene transmission than bacterial clones.