The first report of submandibular lymph node infection with Flavobacterium ceti in a horse and its complete genome sequence.

This is the first report describing the isolation and genome sequence of Flavobacterium ceti (F. ceti IJFC025) from a draining submandibular lymph node abscess in a 6-year-old mixed-breed mare in Korea. Since F. ceti is not a usual infectious pathogen that causes equine health problems, this study presents the complete genome sequence of F. ceti isolated from a submandibular lymph node abscess sample in Jeju, South Korea, in 2022. The entire genome sequence of F. ceti IJFC025 consisted of a 3,144,426-bp chromosome with 35.6 % G + C content. Gene prediction revealed that this strain possesses 2909 coding sequences (CDSs), 74 tRNAs, and five rRNAs. Average nucleotide identity analysis of the whole-genome sequence revealed 98.6 %-98.8 % nucleotide identity between F. ceti IJFC025 and F. ceti CECT7184, which was previously isolated from beaked whales. PathogenFinder revealed four different virulence genes in the genome that could potentially cause infections in horses. F. ceti CECT7184 contained genes encoding propionyl-CoA carboxylase, 3-oxoacid CoA-transferase A subunit, and the translation initiation factor IF-1, whereas F. ceti IJFC025 does not. Instead, F. ceti IJFC025 harbors genes encoding deoxyhypusine synthase, whereas F. ceti CECT7184 does not. Antimicrobial susceptibility tests revealed that F. ceti IJFC025 is a multidrug-resistant strain that is resistant to gentamicin, ceftazidime, nalidixic acid, ciprofloxacin, and colistin. However, no resistance genes were detected in the whole-genome sequence. Because of the similarity of the clinical signs with those of strangles, this pathogen needs to be included in the differential diagnosis of submandibular lymphadenopathy in horses.