Zebrafish (Danio rerio) is an excellent model to study
bacterial infections in fish and their treatment. We used zebrafish as a model of
infection for Aeromonas salmonicida subsp. salmonicida (hereinafter A. salmonicida), the causative agent of fish
furunculosis. The
infection process of A. salmonicida was studied by immersion of zebrafish larvae in 2 different doses of the bacteria and the fish mortality was monitored for three days. The bacterium caused a high mortality (65 %) in zebrafish larvae only when they were exposed to a high bacterial concentration (107 bacterial cells/mL). To evaluate the use of fluorescence microscopy to follow A. salmonicida
infection in vivo, two different fluorescent strains generated by labeling an A. salmonicida strain with either, the
green fluorescent protein (GFP), or with a previously reported
siderophore amonabactin-
sulforhodamine B conjugate (AMB-SRB), were used. The distribution of both labeled bacterial strains in the larvae tissues was evaluated by conventional and confocal fluorescence microscopy. The fluorescent signal showed a greater intensity with the GFP-labeled bacteria, so it could be observed using conventional fluorescence microscopy. Since the AMB-SRB labeled bacteria showed a weaker signal, the larvae were imaged using a
laser scanning confocal microscope after 48 h of exposure to the bacteria. Both fluorescent signals were mainly observed in the larvae digestive tract, suggesting that this is the main colonization route of zebrafish for waterborne A. salmonicida. This is the first report of the use of a
siderophore-fluorophore conjugate to study a
bacterial infection in fish. The use of a
siderophore-fluorophore conjugate has the advantage that it is a specific marker and that does not require genetic manipulation of the bacteria.