Characterization and virulence potential of phenotypically diverse Aeromonas veronii isolates recovered from moribund freshwater ornamental fishes of Kerala, India.
In the present study, we investigated the involvement of Aeromonas spp. in eliciting disease outbreaks in freshwater ornamental fishes across the state of Kerala, India. We investigated three incidences of disease, in which the moribund fishes exhibited clinical signs such as haemorrhagic septicemia (in gouramy, Trichogaster sp.), dropsy (in Oscar, Astronotus ocellatus) and tail rot/fin rot (in gold fish, Carassius carassius). Pure cultures (n = 20 from each fish; 60 in total) of Aeromonas spp. were recovered from the abdominal fluid as well as from internal organs of affected fishes, although they could not be identified to species level because of the variations in their phenotypic characters. The molecular fingerprinting of the isolates using Enterobacterial Repetitive Intergenic Consensus PCR proved the genetic diversity of the isolates from the three sites. The phylogenetic trees constructed using concatenated sequences (using 16S rRNA, gyrA, gyrB and rpoD genes) indicated that they were related to Aeromonas veronii. They exhibited marked cytotoxic and haemolytic activity, which were responsible for the pathogenic potential of the isolates. The isolates possessed multiple virulence genes such as enterotoxins (act and alt), haemolytic toxins (aerA and hlyA), genes involved in type III secretion system (ascV, aexT and ascF-ascG), glycerophospholipid-cholesterol acyltransferase (gcat) and a type IV pilus (tapA) gene, as determined by PCR. Virulence of representative isolates to goldfish was also tested, and we found LD(50) values of 10(4.07)-10(5.35) cfu/fish. Furthermore, the organisms could be recovered as pure cultures from the lesions as well as from the internal organs.
National Centre for Aquatic Animal Health, Cochin University of Science and Technology, Fine Arts Avenue, Cochin, 682 016, Kerala, India.
Krishnan
K
Sreedharan
Rosamma
R
Philip
Isaac Sarojani Bright
IS
Singh
D000333:Aeromonas / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity*; D000825:Animal Structures / Q000382:microbiology; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D015373:Bacterial Typing Techniques; D001826:Body Fluids / Q000382:microbiology; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D005393:Fish Diseases / Q000382:microbiology*; D005399:Fishes; D005618:Fresh Water; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology / Q000662:veterinary*; D007194:India; D007928:Lethal Dose 50; D008969:Molecular Sequence Data; D058885:Multilocus Sequence Typing; D010802:Phylogeny; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D037521:Virulence Factors