Abstract
Due to the negative consequences associated with the use of antibiotics, researchers, and food producers have studied alternatives, such as probiotics, for the control of fish diseases. The probiotic properties of yeasts in aquaculture have been scarcely considered. The present study investigated the probiotic properties of local yeast strains for aquaculture application in the protection of bacterial diseases. Yeast strains (n = 15), previously isolated from the intestinal gut of healthy salmonids, yellowtail, and croaker, were evaluated for their protection of zebrafish larvae following a Vibrio anguillarum challenge. We developed an infection model on zebrafish larvae with V. anguillarum, observing rapid mortality (≥50%) 5 days post-immersion challenge. Infection of Tg(Lyz:DsRed)nz50 larvae with fluorescent-marked V. anguillarum showed the oro-intestinal as the natural route of infection concomitant with an inflammatory response of the larvae reflected by neutrophil migration outside the hematopoietic tissue. Thirteen of 15 strains increased the percentage of larvae survival after the V. anguillarum challenge, although no yeast showed in vitro anti-V. anguillarum activity. In a subset of yeasts, we explored yeast–larvae interactions using fluorescent yeast and evaluated larvae colonization by culture analysis. All fluorescent yeasts were located in the gastrointestinal tract until 5 days post-inoculation (dpi). Yeasts reached 103 CFU/larvae at 0 dpi, although the persistence until 5 dpi of the viable yeast in the gut was different among the strains. These results reveal that some yeasts isolated from the gut of fish could be potential probiotics, reducing the mortality associated to V. anguillarum challenge, and suggest that gut colonization could be involved in the protective effect. Future studies should elucidate other mechanisms involved in yeast protection and verify the beneficial effects of probiotic use in commercial fish species.
Highlights
Aquaculture is one of the fastest-growing food producing sectors, providing almost 50% of all fish for human consumption (FAO/WHO, 2014)
Challenge of Zebrafish Larvae with V. anguillarum Figure 1 shows the survival curve of 5 dpf WT larvae exposed to V. anguillarum
Results show that V. anguillarum was highly virulent; for a period of 5 days post-challenge, survival of larvae challenged with V. anguillarum decreased to at least 45% compared to non-inoculated larvae (P < 0.0001)
Summary
Aquaculture is one of the fastest-growing food producing sectors, providing almost 50% of all fish for human consumption (FAO/WHO, 2014). Some strains have antagonistic activities against undesirable bacteria (Hatoum et al, 2012), can stimulate intestine maturation (Tovar et al, 2002), and modulate antioxidant enzyme in host fish (TovarRamírez et al, 2010). Despite their multiple attributes, screening of probiotic properties of yeasts have been mainly focused on a few species: Saccharomyces cerevisiae and, to a lesser extent, Debaryomyces hansenii (Gatesoupe, 2007)
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