Colonisation and transmission of lux-marked and wild-type Aeromonas salmonicida strains in Atlantic salmon (Salmo salar L.)

Abstract

Colonisation and transmission of Aeromonas salmonicida in Atlantic salmon was investigated using wild‐type and lux‐marked strains of A. salmonicida. An initial intra‐peritoneal (i.p.) challenge showed that lux‐marked cells were virulent only when injected at concentrations ≥109 cfu ml−1 and significantly less infective than wild‐type MT463. The low virulence of A. salmonicida MT463 luxAB was probably due to loss of the proteinaceous A‐layer, which is an important virulence factor involved in both intra‐ and inter‐cellular A. salmonicida interactions. During the i.p. challenge, all fish were held in one tank enabling assessment of transfer of lux‐marked A. salmonicida between fish. Lux‐marked cells shed from moribund and dead fish survived in the water column and cross‐infected cohabitant fish. Cross‐infection by A. salmonicida MT463 luxAB was investigated further by carrying out a cohabitation challenge. Lux‐marked cells were recovered in low numbers from gill tissue and skin/mucus of cohabitant fish. Poor adhesion of cells may be due to loss of the A‐layer protein. During a second cohabitation challenge using A‐layer+ and virulent wild‐type strain MT432, between 102 and 107 cells g−1 of fish gill tissue or skin/mucus were isolated. This result confirmed the preliminary observations obtained using lux‐marked A. salmonicida MT463 and suggested that the gill and skin/mucus regions of fish were the main sites for attachment of A. salmonicida. None of the A. salmonicida strains was recovered from fish intestine samples during cohabitation challenges.

Infection routes of Aeromonas salmonicida in rainbow trout monitored in vivo by real‐time bioluminescence imaging

“…(, ), Svendsen & Bøgwald (), Ferguson et al . () could not be confirmed. Still, given the relatively high threshold limit of luminescence detection, an attachment of a low number of bacteria to the skin cannot be ruled out.…”

“…Bioluminescence imaging (BLI) has been applied for monitoring A. salmonicida in dead Atlantic salmon ( Salmo salar ) (Ferguson et al . ). However, requirement for an exogenous addition of aldehyde for BLI visualization and incorporation of luciferase genes into A. salmonicida significantly lowered the virulence of the bacterium (Ferguson et al .…”

“…However, requirement for an exogenous addition of aldehyde for BLI visualization and incorporation of luciferase genes into A. salmonicida significantly lowered the virulence of the bacterium (Ferguson et al . ). First application of BLI for real‐time monitoring of bacteria in live fish was reported by Karsi et al .…”

The involvement of Aeromonas salmonicida virulence factors in bacterial translocation across the rainbow trout, Oncorhynchus mykiss (Walbaum), intestine

“…The gastrointestinal tract, the gill epithelium and the skin have all been considered as entry points for pathogenic bacteria in fish (Inglis, Roberts & Bromage 1993; Grisez, Chair, Sorgeloos & Ollevier 1996; Olsson, Jöborn, Westerdahl, Blomberg, Kjelleberg & Conway 1996; Svendsen & Bøgwald 1997; Ferguson, Bricknell, Glover, Macgregor & Prosser 1998; O’Toole, Von Hofsten, Rosqvist, Olsson & Wolf‐Watz 2004). A. salmonicida has been isolated from the intestine of salmonids (Ringø & Olsen 1999; Lødemel, Mayhew, Myklebust, Olsen, Espelid & Ringø 2001).…”

Biofilm and Sediment are Major Reservoirs of Virulent Aeromonas hydrophila (vAh) in Catfish Production Ponds

“…Aeromonads that are fish pathogens are easily transmitted horizontally by moribund fish that shed large quantities of bacteria into the water column and cross‐infect cohabitant fish (Ferguson et al. ). Studies on A. salmonicida showed that moribund or dead fish could shed up to 10 5 –10 8 CFU/fish per hour (Rose et al.…”