Method development to estimate infection load in aquaculture
The aim of the pilot project was to create a DNA probe that binds to the genetic material of the fish-causing bacteria Flavobacterium psychrophilum and Aeromonas salmonicida, a subspecies of achromogenes, which can be detected using microscopy (FISH) and flow cytometry. One selective DNA probe for the bacterium F. psychrophilum was created with a combination of two and used with great success to screen for the bacterium using microbial and FISH technology. Specific DNA sensors could not be generated for A. Salmonicida, a subspecies of achromogenes, as its identification gene (16S rDNA) is too similar to other non-infectious Aeromans species. It will be necessary to develop new tentacles that are unique to A. Salmonicida, a subspecies of achromogenes. The flow cytometry is a very fast tool for detecting the binding of specific DNA sensors to microorganisms, which makes the device very suitable for detecting pathogenic bacteria in water. Quantitative analysis of bacteria with such technology is subject to various shortcomings, but it still gives a very good indication of the condition of the water in the fire so that the infection burden can be assessed. The results of this preliminary project show that it is possible to assess the infection burden in aquaculture quickly, but it is necessary to further develop and verify the methodology in real conditions in aquaculture. This was assumed at the beginning of this preliminary project and the participants have applied for a continuation grant to AVS based on the current results and the methodology will be tested under real conditions in charr farming.
The aim of this proof-of-concept study was the development and application of molecular probes for the fish pathogens Flavobacterium psychrophilum and Aeromonas salmonicida subsp. achromogenes, and their detection through Fluorescence In Situ Hybridization (FISH) and flow cytometry. A combination of two species-specific FISH probes was successfully used in combination with flow cytometry to identify and detected F. psychrophilum strains. It was not possible to find specific FISH probes for A. salmonicida subsp. achromogenes. The bacterium is too similar to other Aeromonas species in its 16S rRNA gene sequence and does not contain suitably unique regions that could have been used to develop a species-specific FISH probe. Flow cytometry offers a fast detection system for FISH probes, although technological limitations make reliable quantification difficult. The system is therefore best suited as a semi-quantitative early warning system for emerging fish pathogens in water samples from aquaculture tanks. The results of this preliminary project show that it is possible to estimate the infection load for certain pathogens in aquaculture rapidly but it is necessary to develop the methodology further and test it under real aquaculture conditions. The participants have applied to AVS for new funding based on these results; to develop our rapid methodology further, expand it to more pathogens and test it under real aquaculture conditions.