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The lined seahorse (Hippocampus erectus) is a major cultured seahorse species with significant economic value in China. Bacterial diseases frequently occur in intensive aquaculture environments, among which skin ulceration is one of the most detrimental diseases affecting H. erectus farming. Skin ulceration is mainly caused by Vibrio spp., while the pathogen complexity and diversity remain unclear. [Objective] This study identified dominant bacterial strains from ulcerative lesions of H. erectus in Zhangzhou, Fujian and characterized their pathogenicity, antibiotic resistance profiles, and virulence traits, aiming to provide a scientific basis for disease prevention and control. [Methods] Bacteria were isolated from ulcerated and internal tissue samples of diseased seahorses. Species identification was performed via morphological observation, physiological-biochemical tests, 16S rRNA gene phylogenetic analysis, and reinfection of seahorses. The isolates were cultured for the measurement of hemolytic activity, caseinase production, and salinity tolerance. Ten virulence genes were detected by PCR. The susceptibility of the isolates to 30 antibiotics was tested via the disk diffusion method. Artificial infection was performed with zebrafish as a model to determine the median lethal dose (LD50). [Results] Fifteen dominant strains were isolated from various tissue samples of diseased seahorses. Among them, three strains (HCE003, HCE070, and HCE098) exhibited β-hemolysis and high overall antibiotic resistance rates (50.0%-56.7%). HCE003 carried vvh, pPHDD1, and hlyAch, while both HCE070 and HCE098 carried hlyA, trh, hlyAch, and vhh. HCE003, HCE070, and HCE098 were preliminarily identified as highly pathogenic strains and were further characterized as Citrobacter freundii, Shewanella algae, and Vibrio rotiferianus, respectively. The three strains were capable of growing normally at the salinity of 15‰. Artificial challenge tests demonstrated that they could induce skin ulceration in H. erectus upon reinfection. The median lethal doses of HCE003, HCE070, and HCE098 in zebrafish were 1.71×105 CFU/mL, 3.68×105 CFU/mL, and 2.51×106 CFU/mL, respectively. [Conclusion] This study is the first to report the isolation of multidrug-resistant and highly virulent C. freundii and S. algae from H. erectus with skin ulceration, indicating that non-Vibrio pathogens can also contribute to skin ulceration in seahorses. These findings provide scientific support for the development of targeted disease management strategies and therapeutic agents in seahorse aquaculture.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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