Isolation and characterization of virulent Aeromonas veronii from ascitic fluid of oscar Astronotus ocellatus showing signs of infectious dropsy

Abstract

The cichlid oscar Astronotus ocellatus has worldwide commercial value in the pet fish industry because of its early maturation, relatively high fecundity, ability to identify its caretaker and also to alter colouration amongst conspecifics. Pathogenic strains of Aeromonas veronii resistant to multiple antibiotics were isolated from A. ocellatus individuals showing signs of infectious abdominal dropsy. The moribund fish showed haemorrhage in all internal organs, and pure cultures could be obtained from the abdominal fluid. The isolates recovered were biochemically identified as A. veronii biovar sobria and genetically confirmed as A. veronii based on 16S rRNA gene sequence analysis (GenBank accession no. FJ573179). The RAPD profile using 3 primers (OPA-3, OPA-4 and OPD-20) generated similar banding patterns for all isolates. They displayed cytotoxic and haemolytic activity and produced several exoenzymes which were responsible for the pathogenic potential of the isolates. In the representative isolate MCCB 137, virulence genes such as enterotoxin act, haemolytic toxin aerA, type 3 secretion genes such as aexT, ascV and ascF-ascG, and gcat (glycerophospholipidcholesterol acyltransferase) could be amplified. MCCB 137 exhibited a 50% lethal dose (LD 50 ) of 10 5.071 colony-forming units ml -1 in goldfish and could be subsequently recovered from lesions as well as from the internal organs. This is the first description of a virulent A. veronii from oscar. KEY WORDS: Aeromonas veronii · Oscar · Astronotus ocellatus · Virulence · Ornamental fishesResale or republication not permitted without written consent of the publisher

Characterization and antimicrobial susceptibility of motile aeromonads isolated from freshwater ornamental fish showing signs of septicaemia

“…In contrast, we found A. veronii (79.2%) to be the predominant species which is in agreement with others who reported the dominance of A. veronii among fish pathogenic aeromonad isolates following molecular identification (Sreedharan et al 2011, 2013, Hu et al 2012, Yi et al 2013. This difference could possibly be related to the host species selected and the geographical location, but it may have been due, at least in part, to the methods of bacterial identification employed.…”

Biochemical and Molecular Characterization of Aeromonas Species Isolated from Fish

“…Unlike phenotypic and biochemical identification, which can be modified by the variability of expression of characters, the 16S rDNA sequencing provides unambiguous data even for rare isolates, which are reproducible in and between laboratories (Hossain, 2008). Moreover, confirmation of Aeromonas species may be obtained by sequencing the16S RNA gene (Sreedharan et al, 2011). The present work was performed to isolate and identify the causative agent that infecting the cultured Oreochromis niloticus and Ictalurus punctatuscat (channel cat fish) in Egypt, then determination the best antibacterial agents that effective against it in vitro.…”

The isolation frequency of bacterial pathogens from sea bass (Dicentrarchus labrax) in the Southeastern Black Sea

“…piscicida (Hjeltnes and Roberts 1993;Toranzo et al 2005;Austin and Austin 2007b). The three serotypes of Vibrio anguillarum (O1, O2 and O3) have long been an important concern in mariculture around the world, as it affects various species of fish, molluscs, bivalves and crustaceans (Austin and Austin, 2007a;Frans, Michiels, Bossier, Willems, Lievens, Rediers, 2011;Sreedharan, Philip, Singh, 2011). The dependence of V. anguillarum on high salinity suggests that this bacterium may not be a serious pathogen for sea bass in the Black Sea, because of its salinity levels below 18‰.…”