Virulence potential of Aeromonas hydrophila isolated from apparently healthy freshwater food fish

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 LD 50 for 9C strain was 6.81 × 10 4 CFU/mL and 7.62 × 10 5 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.

Adapting to novel environments together: evolutionary and ecological correlates of the bacterial microbiome of the world’s largest cavefish diversification

“…Aeromonas is a major colonizer in the gastrointestinal tract in freshwater fish (Trust et al, 1979;Haruo et al, 1985) and these release numerous proteases, thus aiding in digestion (Pemberton et al, 1997). However, some members of the genus Aeromonas, such as A. hydrophila, are conditionally pathogenic bacteria (Muduli et al, 2021). Although our results did not indicate harmful species of Aeromonas, we found a significant reduction of Aeromonas abundance in the cavefish gut after captivity.…”

Molecular Epidemiology, Virulence Traits and Antimicrobial Resistance Signatures of Aeromonas spp. in the Critically Endangered Iberochondrostoma lusitanicum Follow Geographical and Seasonal Patterns

“…Similarly, low prevalence of gelatinolytic activity has also been observed before [93], as well as equivalent levels of slime production [94,95]. However, prevalence values and trends seem to vary among surveillance studies [90,[95][96][97][98][99], suggesting that virulence signatures of a specific Aeromonas community are the result of an interaction between the community's composition and the environmental factors shaping their habitat. This is possibly why specific associations of variations in prevalence of extracellular products and slime production and selected streams were observed in this study.…”

Aeromonas hydrophila infection induces Toll-like receptor 2 (tlr2) and associated downstream signaling in Indian catfish, Clarias magur (Hamilton, 1822)

“…Our previously isolated Aeromonas hydrophila 9C strain ( Muduli et al, 2020 ) was used as test strain, while Staphylococcus aureus (ATCC 25923) was used as positive control for this experiment. The bacteria were cultured in tryptic-soy broth (TSB) at 37 °C, overnight and total plate count was estimated individually for both the strains before in-vivo challenge.…”