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

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.

Comparative Pathogenicity of Aeromonas spp. in Cultured Red Hybrid Tilapia (Oreochromis niloticus × O. mossambicus)

“…The ability of Aeromonas spp. to thrive in a wide range of temperatures, from 4 • C to 42 • C, and tolerate up to 5.5 g/L NaCl and in a range of pH from 5 to 10 contributes to their widespread distribution [18,19]. Aeromonas spp.…”

Isolation, molecular characterization and antimicrobial susceptibility ofAeromonasspp. obtained from Tiger Grouper (Epinephelus fuscoguttatus) and Marble Goby (Oxyeleotris marmoratus) fish in Sabah, Malaysia

“…Virulence genes alt , aerA , hlyA , dam and ser were only present in A. dhakensis , indicating that A. dhakensis could be potentially more pathogenic than A. caviae and A. rivuli in causing fish infections. A high virulence of A. dhakensis was also reported in studies of experiment challenge using hybrid tilapia, human blood cell lines and mouse infection model (Chen, Lamy, & Ko, 2016; Chen et al., 2014; Soto‐Rodriguez et al., 2018).…”

“…In Malaysia and Singapore, A. dhakensis was the most prevalent species (50% and 41%, respectively) among all aeromonads isolated from clinical samples (Khor et al., 2018; Puthucheary et al., 2012). Aeromonas dhakensis is distributed worldwide and has been recognized as an emerging pathogen for both humans and fish (Chen et al., 2016; Esteve, Alcaide, & Blasco, 2012; Puah et al., 2013; Soto‐Rodriguez et al., 2018).…”

Antibacterial Potential of Caesalpinia coriaria (Jacq) Willd Fruit against Aeromonas spp. of Aquaculture Importance

“…causing ulcers with muscle necrosis, hemorrhages on the body surface and in the base of the fins, anal prolapse, and lesions in the bladder, kidneys, liver, spleen, gall bladder, heart, brain, and intestine [ 12 ]. A. dhakensis , considered a subspecies of A. hydrophila [ 13 ], affects tilapia, in which it causes hemorrhages from the operculum to the pectoral fins, erosions in caudal fins, abdominal distention, anal prolapse, lethargy, and anorexia [ 14 ].…”

“…The resistance of Aeromonas species to different antimicrobials has been reported: A. hydrophila has presented resistance to penicillin, amoxicillin, piperacillin, cephalexin, doxycycline, and teicoplanin [ 15 ], while A. veronii has shown resistance to chloramphenicol, enrofloxacin, and kanamycin [ 16 ]; the resistance of A. dhakensis to erythromycin, amoxicillin, and ampicillin has also been reported [ 14 ].…”