Page 223 - 《水产学报》2026年第2期

2 期 覃晓曼，等：基于全基因组测序分析大口黑鲈鰤诺卡氏菌致病性和耐药性 50 卷

Analysis of pathogenicity and drug resistance of Nocardia seriolae from
Micropterus salmoides based on whole genome sequencing

QIN Xiaoman , ZHU Lin , XIANG Wei , ZHANG Fuxian , LIU Feng , SU Yingbing *
(College of Animal Science and Technology, Yangtze University, Jingzhou 434023, China)

Abstract: Micropterus salmoides is a crucial economic freshwater fish species in China. In recent years, the continuous expan-
sion of its farming scale has been accompanied by increasingly prominent disease issues, which have inflicted significant eco-
nomic losses on the aquaculture industry. In order to clarify the etiology of diseased M. salmoides in a culture base in Jingzhou,
the main symptoms are manifested primarily as dermal ulcers with hemorrhage and white nodules on the visceral surface. In
this study, a dominant bacterium was isolated from the organs of diseased M. salmoides with white nodules. The isolated strain
was identified through a combination of colony morphology, Gram staining, physiological and biochemical characteristics, as
well as sequence analyses of the 16S rRNA gene, secA1 gene, and whole-genome sequencing. The pathogenicity of the isolated
strain was assessed through virulence gene screening, experimental challenge, and histopathological examination. Its antimicro-
bial resistance was evaluated based on biofilm formation ability, resistance gene screening, and antimicrobial susceptibility test-
ing.The dominant bacterium isolated from the diseased fish was identified as N. seriolae and designated as strain NS01. Com-
parative genomic analysis of the isolate NS01 revealed that N. seriolae NS01 from M. salmoides is more closely related to, and
shares higher similarity with, strains originating from marine fish than to those from freshwater fish. The isolated strain NS01
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showed a median lethal concentration (LD50) of 7.5×10 CFU/mL in M. salmoides, with the presence of four virulence genes:
pup, mig, mce 1A, and gapA. The isolated strain NS01 exhibited a moderate capacity for biofilm formation. It demonstrated
susceptibility to eight antimicrobial agents, including gentamicin, neomycin, and chloramphenicol, while showing resistance to
eleven others, such as penicillin, cefazolin, and norfloxacin. Analysis of resistance genes revealed that the isolated strain NS01
is closely related to several N. seriolae strains of marine fish origin, such as UTF1, KH-11, VT-45, and PY-31, at the genetic
level of antimicrobial resistance. This study successfully isolated a strain of N. seriolae from the nodule-afflicted organs of dis-
eased M. salmoides. The pathogenicity and antimicrobial resistance of this isolate were systematically analyzed, and its evolu-
tionary history was elucidated through whole-genome sequencing. These findings provide a theoretical foundation and data
support for investigating the pathogenic and resistance mechanisms of N. seriolae.
Key words: Micropterus salmoides; Nocardia seriolae; pathogenicity; drug resistance; comparative genomics analysis
Corresponding author: SU Yingbing. E-mail: 1960280268@qq.com

Funding projects: Modern Agricultural Industry Technology system Project in Hubei Province (2021Z22023)

中国水产学会主办 sponsored by China Society of Fisheries https://www.china-fishery.cn
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