title: 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, ascVand ascF-ascG, and gcat (glycerophospholipid-cholesterol acyltransferase) could be amplified. MCCB 137 exhibited a 50% lethal dose (LD50) 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.
authors.affiliation: National Centre for Aquatic Animal Health, School of Marine Sciences, Cochin University of Science and Technology, Fine Arts Avenue, Cochin 682 016, Kerala, India.
authors.forename: K
authors.initials: K
authors.lastname: Sreedharan
authors.forename: R
authors.initials: R
authors.lastname: Philip
authors.forename: I S Bright
authors.initials: IS
authors.lastname: Singh
mesh_terms: D000333:Aeromonas / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001202:Ascitic Fluid / Q000382:microbiology*; D023681:Cichlids; D024881:Drug Resistance, Bacterial; D004487:Edema / Q000382:microbiology / Q000662:veterinary; D005393:Fish Diseases / Q000382:microbiology*; D015964:Gene Expression Regulation, Bacterial; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology / Q000662:veterinary*; D010802:Phylogeny; D014774:Virulence
chemical_list: D000900:Anti-Bacterial Agents