Impact of mucin, bile salts and cholesterol on the virulence of Vibrio anguillarum towards gnotobiotic sea bass (Dicentrarchus labrax) larvae

•Mucin, bile salts and cholesterol increase the virulence of Vibrio anguillarum to sea bass.•The host factors increase protease activity and expression of the empA protease.•The host factors increase flagellar motility and expression of flagellum genes.•The host factors increase EPS production and expression of EPS synthesis genes.•The host factors increase biofilm formation.

In this study, we investigated the impact of the host factors mucin, bile salts and cholesterol on the virulence of the economically important aquatic pathogen Vibrio anguillarum towards sea bass larvae. Pretreatment of V. anguillarum with either one of the host factors (at 10 mg l−1) prior to inoculation into the sea bass rearing water increased virulence of the bacterium, although the effect of cholesterol was not significant. Each of the three host factors significantly increased several virulence-related phenotypes in V. anguillarum, i.e. protease activity, flagellar motility, biofilm formation and exopolysaccharide production, whereas there was no effect on growth of the bacterium under these conditions. Furthermore, the host factors increased the expression of genes involved in these phenotypes, i.e. the metalloprotease empA, the flagellar transcriptional regulator fleQ, the flagellin gene flaA, the chemotaxis methyltransferase gene cheR, the exopolysaccharide biosynthesis gene wbfD and the exopolysaccharide export gene wza. Our results indicate that V. anguillarum uses host mucin, bile salts, and cholesterol as cues to promote the expression of several important virulence traits that enhance the success of transmission from one host to another.