Characterization and pathogenicity of Aeromonas veronii associated with mortality in cage farmed grass carp, Ctenopharyn
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ORIGINAL PAPER
Characterization and pathogenicity of Aeromonas veronii associated with mortality in cage farmed grass carp, Ctenopharyngodon idella (Valenciennes, 1844) from the Central Himalayan region of India Sumanta Kumar Mallik . Nupur Joshi . Neetu Shahi . Krishna Kala . Shivam Singh . Abhay Kumar Giri . Kushagra Pant . Suresh Chandra
Received: 12 July 2020 / Accepted: 26 September 2020 Ó Springer Nature Switzerland AG 2020
Abstract In the study, Aeromonas strains (n = 12) were isolated from moribund grass carp fry reared in the cage culture unit from the Central Himalayan region of India. They were identified as Aeromonas veronii, by biochemically and 16S rRNA analysis. The experimental bath infection of grass carp fry was performed using A. veronii GCAFBLC 228, one of the 12 isolates at cell concentrations 106 and 108 CFU mL-1. The infected fry showed varied behavioural characteristics followed by tail rot, black pigmentation and hemorrhage in the body 48–96 h post infection. The post bath challenged demonstrated maximum mortality (23%) at cell concentration 108 CFU mL-1 during 10th and 12th day. Histopathology revealed hypertrophy, hyperplasia, fusion of gill lamellae, detachment and epithelial cell detachment in gill, swelling of hepatocytes, granular deposition in liver and tubular degeneration and yellow pigmented macrophage aggregates in the kidney. The in vitro assays for virulence traits recorded that A. veronii GCAFBLC 228 was b-haemolytic having strong cell surface hydrophobicity (CHS) characteristic ([ 50%), precipitated after boiling, produced slime, non-suicidal and bound to crystal violet. The antibiogram
S. K. Mallik (&) N. Joshi N. Shahi K. Kala S. Singh A. K. Giri K. Pant S. Chandra ICAR-Directorate of Coldwater Fisheries Research, Anusandhan Bhavan, Industrial Area, Bhimtal, 263 136 Nainital, Uttarakhand, India e-mail: [email protected]
showed that the strain was susceptible to ciprofloxacin (5 lg), cefotaxime (30 lg), ceftazidime (30 lg), cefoxitin (30 lg), ceftriaxone (30 lg), chloramphenicol (30 lg) and tetracycline (30 lg). Negative staining transmission electron microscopy revealed presence of the lateral flagellum-like structure and cell adherence possibly could be correlated with the pathogenicity of A. veronii GCAFBLC 228. The further investigation is warranted to study the transmission, pathogenesis and epidemiology of A. veronii GCAFBLC 228 to develop the best health management practice for cage farmed fish. Keywords Emerging pathogen Aeromonas veronii Grass carp Cage culture Antibiogram
Introduction Grass carp, Ctenopharyngodon idella, has had a long history in aquaculture. It is globally, the second largest produced fish in freshwater aquaculture, making it one of the most economically viable fish species. The faster growth rate along with large size, feeding habits and adaptation to low thermal regime makes it one of the most desirable cultivable species in various freshwater culture systems includi
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