Molecular characteristics of CTX-M β-lactamase-producing and quinolone-resistant Escherichia coli among deer in a popular tourist spot in Japan.

Antimicrobial resistance (AMR) is a growing global concern. Clonal lineages of CTX-M β-lactamase-producing (CTXE) and quinolone-resistant (QREC) were disseminated among the deer population in a famous tourist destination (Nara Park; NP) in Japan. The molecular characteristics of CTXE or QREC isolates, which could pose a threat to public health, have not been elucidated. This study aimed to characterize the genetic traits of CTXE and QREC isolates derived from NP deer and compare them with lineages prevalent worldwide. Sixteen CTXE and three QREC isolates recovered from NP deer faeces between 2018 and 2020 were analysed using whole-genome sequencing (WGS). For endemic lineages, phylogenetic trees were constructed against the isolates registered in the EnteroBase database using the core genome SNP scheme. The most prevalent lineage in NP deer was ST3580. Several pandemic lineages, such as sequence type (ST) 38, ST58 and ST117, were included. The QREC lineages prevalent among deer were designated as extra-intestinal pathogenic or uropathogenic (UPEC). Thirteen of the 24 antimicrobial resistance genes (ARGs) were considered high-risk ARG families. Chromosomal integration of was observed in all plasmid-negative isolates. Phylogenetic analysis suggested relationships between NP isolates and isolates sourced from the environment or poultry. ST3580 has a high potential for clonal dissemination. Furthermore, multiple clinically relevant lineages of CTXE and QREC are endemic in NP deer; however, they could be less virulent than isolates belonging to the same lineages, which could cause severe infectious diseases. Further studies are required to investigate the relationship between chromosomal integration of plasmid-encoded genes and the stable propagation of AMR bacteria in wildlife and the environment.