Vibrio misgurnus sp. nov., a new pathogen of cultured loach (Misgurnus anguillicaudatus), closely related to Vibrio cholerae

An epidemic with petechial hemorrhages on the body surface recently occurred in the farmed loach (Misgurnus anguillicaudatus) in Sichuan province. Multiple antibiotic treatments were ineffective against this epidemic. This study aims to elucidate the cause of the disease. Two bacterial strains, GVCT and VCS were isolated from diseased loach. Experimental infections with these two isolates resulted in marked symptoms in the loach consistent with those observed in natural outbreaks. The taxonomic status was determined by phenotypic assay, chemotaxonomic and whole genome analysis. Strain GVCT exhibited unique phenotypic characteristics, including its β-glucosidase activity and inability to utilize casein and starch, which distinguished it from Vibrio cholerae ATCC14035T. Paired 16S rRNA gene sequence analysis confirmed that strains GVCT and VCS belong to the genus Vibrio. The primary fatty acids of strain GVCT are C16:0, summed Feature 3 (C16:1ω7c/C16:1ω6c), and summed Feature 8 (C18:1 ω6c/C18:1 ω7c), and the major respiratory quinone is Q-8. The predominant lipids were phosphatidylethanolamine (PE), phosphatidylglycerol (PG), aminophospholipids (APL) and an unidentified phosphoglycolipid designated PL1. Strains GVCT and VCS have genome sizes of 3.2 Mb and 3.3 Mb, as well as GC contents of 47.0 and 47.2 mol% respectively. Phylogenomic and whole-genome nucleotide sequence analyses further confirmed that these isolates represent a novel species of the genus Vibrio, for which the name Vibrio misgurnus sp. nov. is proposed, with strain GVCT as the type strain. Strain GVCT was found to be highly pathogenic to loach, causing high mortality and posing a threat to loach aquaculture, with a half-lethal dose (LD50) of strain GVCT for loach is 8.96 × 106 CFU/mL, and it was resistant to drugs such as enrofloxacin, doxycycline hydrochloride, flumequine, neomycin sulphate and florfenicol.