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Diseases of Aquatic Organisms

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DAO 129:107-116 (2018)  -  DOI: https://doi.org/10.3354/dao03247

Virulence of the fish pathogen Aeromonas dhakensis: genes involved, characterization and histopathology of experimentally infected hybrid tilapia

S. A. Soto-Rodriguez1,*, R. Lozano-Olvera1, M. T. Garcia-Gasca2, S. M. Abad-Rosales1, B. Gomez-Gil1, J. Ayala-Arellano3

1CIAD, AC Mazatlan Unit for Aquaculture and Environmental Management, 82112 Mazatlan, Sinaloa, Mexico
2Autonomous University of Queretaro, Faculty of Natural Sciences, Campus Juriquilla, 76230 Santiago de Querétaro, Queretaro, Mexico
3Jade Tropical, 82267 Mazatlan, Sinaloa, Mexico
*Corresponding author:

ABSTRACT: Aeromonas dhakensis (Ad) CAIM 1873 growth was evaluated at different conditions and antibiotic susceptibility. Mortality and histopathological damages in hybrid tilapia Oreochromis niloticus × O. mossambicus, and virulence factors caused by Ad bacterial cells and extracellular products (ECPs) were evaluated, and the whole genome was obtained. Ad grew between 0.0 and 5.5% NaCl at a pH of between 4 and 10 and from 4 to 37°C. The lowest minimum inhibitory concentration was found for enrofloxacin (<5 µg ml-1), and bacteria were resistant to erythromycin, amoxicillin and ampicillin. Ad bacterial cells (1.86 × 105 cells g-1) and ECPs (0.462 µg protein fish-1) were highly virulent to challenged hybrid tilapia and caused over 80% mortality at 24 h. The primary clinical sign caused was haemorrhage, and damage was most marked in the spleen, liver, kidney and brain of fish challenged with bacterial cells. To our knowledge, this is the first report that Ad causes pyknotic and karyorrhectic nuclei of erythrocytes in the internal organs of hybrid tilapia, which was the most striking histopathological observation. The virulence of Ad to hybrid tilapia may be primarily related to the activity of haemolysins (hlyA genes) and cytotoxins (aerolysin aerA), along with the production of siderophores and proteases. We also found β-lactamase, tetracycline and multiple antibiotic resistance genes, as well as adherence, iron acquisition, toxins (aerolysin family, haemolysins) and diverse protease genes.


KEY WORDS: Aeromonas dhakensis · Virulence · Erythrocyte necrosis · Antibiotic · Virulence genes · Oreochromis


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Cite this article as: Soto-Rodriguez SA, Lozano-Olvera R, Garcia-Gasca MT, Abad-Rosales SM, Gomez-Gil B, Ayala-Arellano J (2018) Virulence of the fish pathogen Aeromonas dhakensis: genes involved, characterization and histopathology of experimentally infected hybrid tilapia. Dis Aquat Org 129:107-116. https://doi.org/10.3354/dao03247

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