Molecular characterization of extended spectrum cephalosporin resistant isolated from livestock and in-contact humans in Southeast Nigeria.

The rise in antimicrobial resistance (AMR) in bacteria is reducing therapeutic options for livestock and human health, with a paucity of information globally. To fill this gap, a One-Health approach was taken by sampling livestock on farms ( = 52), abattoir ( = 8), and animal markets ( = 10), and in-contact humans in Southeast Nigeria. Extended spectrum cephalosporin (ESC)-resistant (ESC-R) was selectively cultured from 975 healthy livestock faecal swabs, and hand swabs from in-contact humans. Antimicrobial susceptibility testing (AST) was performed on all ESC-R . For isolates showing a multi-drug resistance (MDR) phenotype ( = 196), quantitative real-time PCR (qPCR) was performed for confirmation of extended-spectrum β-lactamase (ESBL) and carbapenemase genes. Whole-genome sequencing (WGS) was performed on a subset ( = 157) for detailed molecular characterisation. The results showed ESC-R was present in 41.2% of samples, with AST results indicating 48.8% of isolates were phenotypically MDR. qPCR confirmed presence of ESBL genes, with present in all but others in a subset [ (62.8%) and (0.5%)] of isolates; none harboured transferable carbapenemase genes. Multi-locus sequence typing identified 34 Sequence Types (ST) distributed among different sampling levels; ST196 carrying was predominant in chickens. Large numbers of single nucleotide polymorphisms (SNPs) in the core genome of isolates, even within the same clade by phylogenetic analysis, indicated high genetic diversity. AMR genotyping indicated the predominant variant was (87.9%), although , and were present; it was notable that , common in livestock, was absent. Other predominant AMR genes included: 2, S1, B, , A-v2, and A14, with prevalence varying according to host livestock species. A harbouring plasmid from livestock isolates in Ebonyi showed high sequence identity to one from river/sewage water in India, indicating this ESBL plasmid to be globally disseminated, being present beyond the river environment. In conclusion, ESC-R was widespread in livestock and in-contact humans from Southeast Nigeria. WGS data indicated the isolates were genetically highly diverse, probably representing true diversity of wild type ; they were likely to be MDR with several harbouring Surprisingly, human isolates had highest numbers of AMR genes and pigs the least.