Virulence potential of Aeromonas hydrophila isolated from apparently healthy freshwater food fish
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ORIGINAL ARTICLE
Virulence potential of Aeromonas hydrophila isolated from apparently healthy freshwater food fish Chinmayee Muduli 1 & Gayatri Tripathi 2 & Kurcheti Paniprasad 2 & Kundan Kumar 2 & Rajeev Kumar Singh 1 & Gaurav Rathore 1 Received: 9 April 2020 / Accepted: 23 October 2020 # Institute of Molecular Biology, Slovak Academy of Sciences 2020
Abstract Aeromonas hydrophila is considered an important pathogen of fish causing substantial economic loss in aquaculture worldwide. The objective of the current study was to assess the virulence potential of A. hydrophila strains isolated from gills of apparently healthy fish using phenotypic assays, PCR based genotypic tests, and in-vivo pathogenicity assays in Indian catfish, Clarias magur. For this, motile aeromonads (n = 50) were isolated from gills of apparently healthy freshwater food fish (n = 50) collected from domestic fish market. Gill swabs were incubated for primary enrichment in alkaline peptone water supplemented with cephalothin (10 mg/mL) for 12 hours followed by plating on Starch Ampicillin Agar. A single big yellow colony was selected from each sample, purified, and presumptively identified as Aeromonas with the help of Aerokey-II. Out of the fifty isolates of Aeromonas, five isolates of diverse origin (9C, 10G1, 7C, 10C and 4P) were confirmed to be A. hydrophila by automated bacterial identification system VITEK 2 with confidence interval of 90–98%. In the phenotypic assays, strains 9C and 10G1 showed high serum resistance, swimming and swarming activity and low biofilm producing capabilities, which were indicative of putative virulence. Both the strains belonged to genotype aah+act+ alt+ascV+eno+lip+ast+ on the basis of detection of virulence genes by PCR, i.e. extracellular haemolysin (aah), cytolytic enterotoxin (act), heat-labile cytotonic enterotoxin (alt), type-III secretion system (ascV), enolase (eno), lipase (lip) and heat-stable cytotonic enterotoxin (ast). In-vivo pathogenicity assays confirmed that both the strains were pathogenic to magur fish. The LD50 for 9C strain was 6.81 × 104 CFU/mL and 7.62 × 105 CFU/mL for 10G1strain. In conclusion, our phenotypic and genotypic findings showed that A. hydrophila isolated from apparently healthy fish harbour number of important virulence genes/factors and could have important implications in triggering disease in farmed fish under stress. Keywords Aeromonas hydrophila . Healthy food fish . Virulence genes . LD50
Introduction Aeromonas hydrophila is considered an important bacterial pathogen of fish. Disease outbreaks caused by A. hydrophila result in economic losses in aquaculture (Karunasagar et al. 1989; Pridgeon and Klesius 2011). This pathogen causes Motile Aeromonad Septicaemia (MAS) in farmed and wild fishes. The major signs of MAS are ulcerations on the body * Gaurav Rathore [email protected] 1
ICAR-National Bureau of Fish Genetic Resources (NBFGR), Canal Ring Road, Telibagh, P.O. Dilkusha, Lucknow 226 002, India
2
ICAR-Central Institute of Fisheries Education, Panch Marg, Off
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