Introduction. The global spread of extended-spectrum cephalosporinase-producing Escherichia coli (producing extended-spectrum β-lactamase or plasmid-borne AmpC, hereafter ESC-Ec) is a major public health concern. Whilst extensively studied in high-income countries, the transmission pathways between humans and animals in low- and middle-income countries (LMICs) remain unclear. In rural Cambodia, the asymptomatic carriage and transmission dynamics of ESC-Ec between humans and animals living in close proximity are poorly understood, highlighting the need for targeted research in this area.

Gap statement. An enhanced understanding of the genetic epidemiology of ESC-Ec can enable mitigation strategies to reduce the burden of disease and drug-resistant infections in LMIC settings.

Aim. This study aimed to investigate the genetic relatedness and genotypic antibiotic resistance profiles of ESC-Ec strains from humans and livestock in rural Cambodia and to identify patterns of antimicrobial resistance (AMR) gene transmission between hosts and across households and villages.

Methodology. Faecal samples were collected from 307 humans and 285 livestock in 100 households in or near Kampong Cham Province in rural Cambodia. From these samples, 108 ESC-Ec strains were subjected to whole-genome sequencing. Core genome MLST (cgMLST) and phylogenetic analysis determined genetic relationships between strains. All strains were screened for the presence of antibiotic resistance genes and plasmids.

Results. Human and livestock isolates were assigned to six phylogroups, with phylogroup A being the most common (56.5%). MLST identified 50 sequence types (STs), 17 of which were shared between humans and animals, with ST155 being the most prevalent. cgMLST revealed 97 distinct cgMLST sequence types (cgST), indicating strain sharing between humans and animals. Additionally, AMR gene analysis showed widespread resistance, with genes from the blaCTX-M group detected in 84.2% of isolates. Notably, AMR genes such as aph(3'')-Ib–sul2 co-occurred in 50% of isolates. Finally, plasmid analysis identified IncF plasmids in 75.9% of isolates, likely facilitating AMR gene transmission across hosts.

Conclusions. Our findings demonstrate that ESC-Ec strains and their AMR genes are transmitted between humans and livestock in rural Cambodia, likely driven by both clonal spread and plasmid-mediated horizontal gene transfer. These results highlight the urgent need for antimicrobial stewardship and infection control strategies to mitigate the spread of multidrug-resistant pathogens in both human and animal populations.