Virulence traits and gene profiles of Vibrio alginolyticus from farmed red drum in Vietnam

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Published: 2026-03-09
DOI: https://doi.org/10.13057/biodiv/d270145
Keywords:
Aquaculture diseases, hemorrhagic disease, pathogenicity genes, Southeast Asian aquaculture, Vibrio alginolyticus
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NGUYEN NAM QUANG
Faculty of Fisheries, University of Agriculture and Forestry, Hue University. 102 Phung Hung St., Hue City, Vietnam
NGUYEN DUC QUYNH ANH
Faculty of Fisheries, University of Agriculture and Forestry, Hue University. 102 Phung Hung St., Hue City, Vietnam
NGUYEN THI HUE LINH
Faculty of Fisheries, University of Agriculture and Forestry, Hue University. 102 Phung Hung St., Hue City, Vietnam
CAROLA VENTURINI
Sydney School of Veterinary Science, Faculty of Science, University of Sydney. McMaster Building (B14), NSW 2006, Australia
FRANSISCA SAMSING
Sydney School of Veterinary Science, Faculty of Science, University of Sydney. McMaster Building (B14), NSW 2006, Australia
NGUYEN NGOC PHUOC ♥
Faculty of Fisheries, University of Agriculture and Forestry, Hue University. 102 Phung Hung St., Hue City, Vietnam

Abstract

Abstract. Quang NN, Anh NDQ, Linh NTH, Venturini C, Samsing F, Phuoc NN. 2026. Virulence traits and gene profiles of Vibrio alginolyticus from farmed red drum in Vietnam. Biodiversitas 27 (1): d270145. https://doi.org/10.13057/biodiv/d270145. Vibrio alginolyticus is an emerging bacterial pathogen associated with hemorrhagic disease and mortality in red drum (Sciaenops ocellatus) and other marine fish species. This study investigated virulence phenotypes and virulence-associated gene profiles of V. alginolyticus isolates infecting red drum, which is strain-dependent and reflects the combined expression of multiple phenotypic traits rather than the presence of individual virulence genes alone. Twenty V. alginolyticus isolates obtained from diseased red drum farmed in Hue City, central Vietnam, were evaluated for swimming motility, extracellular enzyme activity, and biofilm formation, and a composite virulence score was calculated using min-max normalized phenotypic data. Based on these scores, ten high-ranking isolates were selected for PCR screening of sixteen virulence-associated genes. Marked phenotypic variability was observed among isolates, with motility and extracellular enzyme activity contributing most strongly to virulence differentiation, whereas biofilm formation was generally weak to moderate. Fifteen genes were detected, including flagellar and motility-related genes (flaA, flaC, flgE, flrA, flrB, flrC, and flaK), hemolysin-related genes (trh and tlh), an adhesion gene (tcpA), secretion system components (vopB, vopD, and vgrG), and iron-acquisition genes (pvuA and pvsA), whereas tdh was not detected. Among the isolates, VA15 and VA17 exhibited the highest motility and extracellular enzyme activities, while most isolates formed weak but detectable biofilms. Pathogenicity testing confirmed that isolate VA15, identified as the most virulent based on in vitro profiling, caused dose-dependent mortality in red drum, with an LD50 of 4.0 × 104 CFU/fish (95% CI: 3.2 × 104-5.1 × 104 CFU/fish). Overall, this study provides baseline phenotypic and molecular data on V. alginolyticus infecting farmed red drum in central Vietnam and contributes to understanding virulence variability among isolates in marine cage aquaculture systems.

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Vol. 27 No. 1 (2026)

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Author Biographies

NGUYEN NAM QUANG, Faculty of Fisheries, University of Agriculture and Forestry, Hue University. 102 Phung Hung St., Hue City, Vietnam

University of Agriculture and Forestry, Hue University

NGUYEN DUC QUYNH ANH, Faculty of Fisheries, University of Agriculture and Forestry, Hue University. 102 Phung Hung St., Hue City, Vietnam

University of Agriculture and Forestry, Hue University,

NGUYEN THI HUE LINH, Faculty of Fisheries, University of Agriculture and Forestry, Hue University. 102 Phung Hung St., Hue City, Vietnam

University of Agriculture and Forestry, Hue University

CAROLA VENTURINI, Sydney School of Veterinary Science, Faculty of Science, University of Sydney. McMaster Building (B14), NSW 2006, Australia

Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Camden, New South Wales, Australia

FRANSISCA SAMSING, Sydney School of Veterinary Science, Faculty of Science, University of Sydney. McMaster Building (B14), NSW 2006, Australia

 

Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Camden, New South Wales, Australia

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