Hubei Key Laboratory of Animal Nutrition and Feed Science, School of Animal Science and Nutritional Engineering, Wuhan Polytechnic University, Wuhan, 430023, China.
Zhejiang Fisheries Technical Extension Center, and Zhejiang Fisheries Test and Aquatic Disease Prevention Center, Hangzhou, 310023, China.
Microb Pathog. 2022 Dec;173(Pt A):105815. doi: 10.1016/j.micpath.2022.105815. Epub 2022 Oct 7.
Largemouth bass (Micropterus salmoides) is an important commercial fish species that is widely cultured throughout China. With the application of high-density culture, M. salmoides is usually infected by different pathogens in water. Particularly, co-infection with multiple pathogens was common, which has considerably outweighed the impact caused by single infections. In this research, two bacteria strains were isolated from diseased fish by incubating on brain heart infusion agar. According to the results of 16S rRNA and gyrB sequence, as well as the analysis of morphological, physiological and biochemical features, the isolated bacterial strains were finally identified as Aeromonas veronii and Nocardia seriolae, respectively. In addition, eight virulence genes related to pathogenicity including enterotoxin, lipase, elastase, quorum sensing, hemolysin and adhesion were identified in A. veronii isolate and eight virulence genes encoding mammalian cell entry family proteins, glyceraldehyde-3-phosphate dehydrogenase, mycolyltransferase, nitrate reductase subunits, and putative cytotoxin/hemolysin were detected in N. seriolae isolate. Drug sensitivity testing indicated that both A. veronii and N. seriolae isolates were susceptible to kanamycin, streptomycin, gentamycin, neomycin, doxycycline, tetracycline, ciprofloxacin and levofloxacin, and resistant to amikacin, cefpimizole, ampicillin, piperacillin, carbenicillin, oxacillin, rifampicin, trimethoprim, vancomycin, meropenem, imipenem and sulfisoxazole. Moreover, serious histopathological changes, such as typical granulomas with necrotic center, cell degeneration and necrosis, hemorrhage and inflammatory cell infiltration, were found in the naturally diseased fish. The LD of A. veronii and N. seriolae isolates were 7.94 × 10 CFU/g and 3.16 × 10 CFU/g fish weight, respectively. In addition, the coinfection of A. veronii and N. seriolae induce quick and higher mortality in comparison with those challenged by single bacteria. These results revealed that both A. veronii and N. seriolae participated in the disease outbreaks of the M. salmoides, and concurrent of those two bacteria synergistically exacerbate the disease severity.
大口黑鲈（Micropterus salmoides）是中国广泛养殖的一种重要商业鱼类。随着高密度养殖的应用，大口黑鲈通常会在水中感染不同的病原体。特别是，多种病原体的混合感染较为常见，其影响远远超过单一感染。在这项研究中，通过在脑心浸液琼脂上孵育，从患病鱼体中分离出两种细菌菌株。根据 16S rRNA 和 gyrB 序列的结果以及形态学、生理和生化特征的分析，这两种分离的细菌菌株最终分别被鉴定为维氏气单胞菌和海鱼诺卡氏菌。此外，在维氏气单胞菌分离株中鉴定出与致病性相关的 8 种毒力基因，包括肠毒素、脂肪酶、弹性蛋白酶、群体感应、溶血素和黏附素，而在海鱼诺卡氏菌分离株中检测到 8 种编码哺乳动物细胞进入家族蛋白、甘油醛-3-磷酸脱氢酶、(mycolyltransferase)、硝酸还原酶亚基和推定细胞毒素/溶血素的毒力基因。药敏试验表明，维氏气单胞菌和海鱼诺卡氏菌分离株均对卡那霉素、链霉素、庆大霉素、新霉素、强力霉素、四环素、环丙沙星和左氧氟沙星敏感，对阿米卡星、头孢匹肟、氨苄西林、哌拉西林、羧苄西林、苯唑西林、利福平、甲氧苄啶、万古霉素、美罗培南、亚胺培南和磺胺异噁唑耐药。此外，在自然患病鱼中发现了严重的组织病理学变化，如具有坏死中心的典型肉芽肿、细胞变性和坏死、出血和炎症细胞浸润。维氏气单胞菌和海鱼诺卡氏菌分离株的 LD 分别为 7.94×10 CFU/g 和 3.16×10 CFU/g 鱼体重。此外，与单一细菌感染相比，维氏气单胞菌和海鱼诺卡氏菌的混合感染导致死亡率更快更高。这些结果表明，维氏气单胞菌和海鱼诺卡氏菌都参与了大口黑鲈疾病的暴发，并且这两种细菌的共存协同加剧了疾病的严重程度。
