Citrobacter freundii induced pathogenicity towards fish: an insight investigation through serum biochemistry and gene expression analysis in Labeo rohita
{"title":"Citrobacter freundii induced pathogenicity towards fish: an insight investigation through serum biochemistry and gene expression analysis in Labeo rohita","authors":"Souvik Dhar, Arup Mistri, Ajaya Kumar Rout, Kampan Bisai, Basanta Kumar Das, Bijay Kumar Behera","doi":"10.1007/s10499-025-02222-2","DOIUrl":null,"url":null,"abstract":"<div><p><i>Citrobacter freundii</i>, a frequent freshwater fish pathogen leads to considerable economic losses in the global aquaculture industry. In this study, the virulence property of <i>C. freundii</i> (NCBI accession number: PP112336) was done through in vitro and in vivo approaches. Scanning electron microscopy revealed that it is an elongated, rod-shaped bacterium having high proficiency in biofilm production. The results of biochemical characterization exhibited high similarities with previously reported biochemical characteristics of <i>C. freundii</i>. Antibiotic susceptibility test highlighted that the isolate has a multiple antibiotic resistance capability (MAR index: 0.25). Haemolytic activity, biofilm assay, swimming motility, and cytotoxicity study indicated its highly pathogenic capability. Next, in vivo virulence screening was done by injecting pure culture of <i>C. freundii</i> in healthy fingerlings of <i>L. rohita</i>. The 96 h LD<sub>50</sub> value of this isolate was found to be approximately 1.2 × 10<sup>4</sup> CFU/fish. Further, 100 times lower sublethal dose to LD<sub>50</sub> (1.2 × 10<sup>2</sup> CFU/fish) of the isolate was administrated in fingerlings to evaluate immunomodulatory effects on the host. Immune and stress-response biomarkers, such as SOD, IgM, and catalase levels were significantly decreased, while cortisol, HSP70, and HSP90 levels were significantly elevated with post injection duration in infected fish. The analysis of mRNA expression of immune-related genes, including <i>TLR4</i>, <i>TNF-α</i>, <i>HSP70</i>, <i>C3</i>, <i>NOD1</i>, and <i>IL-1β</i> showed significant alternations in the liver, kidney, and skin tissues of injected fingerlings over the infection duration. These changes indicated the response of fish to counteract the immunological damage caused by bacterial invasion. This study offers valuable insights to understand the infection process as well as in the development of therapies to control the infection.</p><h3>Graphical Abstract</h3>\n<div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":8122,"journal":{"name":"Aquaculture International","volume":"33 6","pages":""},"PeriodicalIF":2.4000,"publicationDate":"2025-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Aquaculture International","FirstCategoryId":"97","ListUrlMain":"https://link.springer.com/article/10.1007/s10499-025-02222-2","RegionNum":3,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"FISHERIES","Score":null,"Total":0}
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Abstract
Citrobacter freundii, a frequent freshwater fish pathogen leads to considerable economic losses in the global aquaculture industry. In this study, the virulence property of C. freundii (NCBI accession number: PP112336) was done through in vitro and in vivo approaches. Scanning electron microscopy revealed that it is an elongated, rod-shaped bacterium having high proficiency in biofilm production. The results of biochemical characterization exhibited high similarities with previously reported biochemical characteristics of C. freundii. Antibiotic susceptibility test highlighted that the isolate has a multiple antibiotic resistance capability (MAR index: 0.25). Haemolytic activity, biofilm assay, swimming motility, and cytotoxicity study indicated its highly pathogenic capability. Next, in vivo virulence screening was done by injecting pure culture of C. freundii in healthy fingerlings of L. rohita. The 96 h LD50 value of this isolate was found to be approximately 1.2 × 104 CFU/fish. Further, 100 times lower sublethal dose to LD50 (1.2 × 102 CFU/fish) of the isolate was administrated in fingerlings to evaluate immunomodulatory effects on the host. Immune and stress-response biomarkers, such as SOD, IgM, and catalase levels were significantly decreased, while cortisol, HSP70, and HSP90 levels were significantly elevated with post injection duration in infected fish. The analysis of mRNA expression of immune-related genes, including TLR4, TNF-α, HSP70, C3, NOD1, and IL-1β showed significant alternations in the liver, kidney, and skin tissues of injected fingerlings over the infection duration. These changes indicated the response of fish to counteract the immunological damage caused by bacterial invasion. This study offers valuable insights to understand the infection process as well as in the development of therapies to control the infection.
期刊介绍：
Aquaculture International is an international journal publishing original research papers, short communications, technical notes and review papers on all aspects of aquaculture.
The Journal covers topics such as the biology, physiology, pathology and genetics of cultured fish, crustaceans, molluscs and plants, especially new species; water quality of supply systems, fluctuations in water quality within farms and the environmental impacts of aquacultural operations; nutrition, feeding and stocking practices, especially as they affect the health and growth rates of cultured species; sustainable production techniques; bioengineering studies on the design and management of offshore and land-based systems; the improvement of quality and marketing of farmed products; sociological and societal impacts of aquaculture, and more.
This is the official Journal of the European Aquaculture Society.
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