Evaluation of probiotic effect of Aeromonas hydrophila on the development of the digestive tract of germ-free Artemia franciscana nauplii

Gnotobiotic model systems are attracting attention as they facilitate the unraveling of mechanisms involved in host–microbe interactions. Here morphological and stereological tools were incorporated to contribute to the study on the mode of action of putative probiotic bacteria. In this study, the effect of live probiotic bacteria on the early development of the digestive tract of gnotobiotic Artemia franciscana was investigated. Germ-free Artemia nauplii were cultured for 6 days using Baker's yeast and dead Aeromonas hydrophila (LVS3, a putative probiotic strain for Artemia franciscana) as major feed sources. For the other group, live Aeromonas hydrophila was added on day 1 (day of hatching), while all the other parameters were analogous to the germ-free group. The survival on day 6 was significantly higher in the group in which live probiotic bacteria were used than in the control group. Individual length and total biomass production were always significantly larger in the same group. Midgu volume/individual length and the midgut length/individual length were not significantly different between both groups on all the sampling points. Hindgut volume/individual length and the hindgut length/individual length were not significantly different between both the groups on days 2 and 4 while those were significantly larger at day 6 in the cultures fed with live bacteria, suggesting that live bacteria have a positive effect on cell proliferation in the gut. However, the morphology of the mid- and the hindgut did not show important differences between both groups.