Related Experiment Video
Updated: May 22, 2026
Modeling Persistent Pseudomonas aeruginosa Infection in Wounded Zebrafish Larvae
Published on: June 13, 2025
Pseudomonas M162 confers protection against rainbow trout fry syndrome by stimulating immunity
T L Korkea-aho1, A Papadopoulou, J Heikkinen
1Institute of Aquaculture, University of Stirling, Stirling, UK. tiina.korkea-aho@evira.fi
Aims:
To evaluate the antagonistic effect of Pseudomonas M162 against Flavobacterium psychrophilum.
Methods And Results:
The antagonistic activity of M162 was tested in vivo and in vitro, and its mode of action examined by siderophore production and immunological responses of rainbow trout (Oncorhynchus mykiss) fry. Pseudomonas M162 inhibited the growth of Fl. psychrophilum in vitro and increased the resistance of the fish against the pathogen, resulting in a relative per cent survival (RPS) of 39·2%. However, the siderophores produced by M162 did not have an inhibitory effect on Fl. psychrophilum. In fish fed with M162, the probiotic colonized the gastrointestinal tract and stimulated peripheral blood leucocyte counts, serum lysozyme activity and total serum immunoglobulin levels after 3 weeks from the start of feeding.
Conclusions:
This study showed the potential of Pseudomonas M162 as a probiotic by reducing the mortalities that occurred during an experimental Fl. psychrophilum infection, resulting mainly through the immunostimulatory effects of the bacterium.
Significance And Impact Of The Study:
Rainbow trout fry syndrome (RTFS) causes high mortalities during the early life stages of the fish's life cycle, partly because their adaptive immunity has not yet fully developed. Thus, immunomodulation by probiotics could be an effective prophylactic method against RTFS.
Insights
Pseudomonas M162 shows potential as a probiotic, reducing mortalities in rainbow trout fry infected with Flavobacterium psychrophilum. Its benefits stem primarily from stimulating the fish
Area of Science:
- Aquatic animal health
- Microbiology
- Immunology
Background:
- Rainbow trout fry syndrome (RTFS) causes significant mortality in young fish due to underdeveloped adaptive immunity.
- Probiotic immunomodulation offers a potential prophylactic strategy against RTFS.
Purpose of the Study:
- To evaluate the antagonistic effect of Pseudomonas M162 against Flavobacterium psychrophilum.
- To assess the efficacy of Pseudomonas M162 as a probiotic in rainbow trout fry.
Main Methods:
- In vitro and in vivo testing of Pseudomonas M162 against Flavobacterium psychrophilum.
- Examination of siderophore production and immunological responses in rainbow trout fry.
- Monitoring of gastrointestinal colonization and immune parameters in fish fed with M162.
Main Results:
- Pseudomonas M162 inhibited Flavobacterium psychrophilum growth in vitro and increased fish resistance, achieving a 39.2% relative percent survival (RPS).
- Siderophore production by M162 did not inhibit Flavobacterium psychrophilum.
- M162 administration stimulated leucocyte counts, serum lysozyme activity, and immunoglobulin levels in fish.
Conclusions:
- Pseudomonas M162 demonstrates potential as a probiotic for reducing mortalities associated with Flavobacterium psychrophilum infections.
- The primary mechanism appears to be immunostimulatory effects, enhancing the fish's immune response.
