A. salmonicida infection inhibits rainbow trout gill mucin production

The gills are a critical organ and the primary site of colonization with the pathogen Aeromonas salmonicida. They are covered by protective mucus, mainly comprised by the highly glycosylated mucins. The aim of this study was to characterize the rainbow trout (Oncorhynchus mykiss) gill mucus and mucin production during health and colonization with A. salmonicida. Ex vivo imaging of gill mucus demonstrated that it was heterogenous in its glycosylation and organized in strands. Metabolic labelling time-course experiments in vivo revealed that the metabolic label was incorporated into mucins in the perinuclear region of interlamellar mucus producing cells at 4 h post intraperitoneal injection of the label. The newly produced mucin gradually moved through the mucus theaca, and by 20 h the majority of the labelled mucin was in the apical compartment of the cell. A. salmonicida colonization decreased mucin production in the gills during early time points (8 and 32 h post immersion [PI]) in 10⁸A. salmonicida/mL for 1 h and mucin production recovered by day 7 PI, coinciding with decreased A. salmonicida density. No significant effect on the mucin production was detected in fish immersed in 10⁷A. salmonicida/mL. A. salmonicida also decreased mucin production in an RTgill-W1 based in vitro mucosal surface, demonstrating that the pathogen directly can inhibit mucin production. Thus, A. salmonicida can inhibit gill mucin production, but mild colonization did not have significant effects on the gill mucus production. Possibly, restoring or enhancing mucin production may provide an avenue to combat infection in aquaculture.