First report of a Brucella inopinata-like atypical Brucella strain isolated from a waxy monkey treefrog (Phyllomedusa bicolor) in the Republic of Korea: Case Report

Atypical Brucella spp., which include Brucella inopinata and related lineages, have emerged as unconventional pathogens with an expanding host range, particularly among exotic amphibians. A captive waxy monkey treefrog (Phyllomedusa bicolor) presented with a focal ulcerative skin lesion above its right eye. Cytology revealed mixed inflammation associated with a bacterial infection, and 16S rRNA sequencing identified the isolate as a member of the Brucella genus. Whole-genome sequencing using hybrid PacBio–Illumina platforms generated a high-quality draft genome. Average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values demonstrated the highest similarity to B. inopinata (98.08% ANI; 83.50% dDDH). Core genome phylogenetic analysis further confirmed close clustering with atypical Brucella spp., which are clearly distinct from classical zoonotic lineages. This case represents the first detection of an atypical B. inopinata-like Brucella strain in an amphibian in the Republic of Korea.