Not another review of probiotics..

Inspired by todays lecture I am going to introduce one last paper about the impact of probiotics on fish performance. Probiotics feed as diet additives can benefit treated organisms in several ways. Previous studies have shown greater growth performance by improving digestive tract conditions and intestinal activity. It has been also found that probiotics can reduce the presence of pathogens. Further, probiotics have the potential to improve disease resistance by enhancing immunological responses. 

The study by Gioacchini et al. (2014) looked into the impact of probiotics on the immune response of the zebrafish (Danio rerio). Effects of a diet containing the probiotic Lactobacillus rhamnosus IMC 501 on innate immune responses and hepatic stress were investigated. Two experimental groups were analysed. The control group were fed with a usual diet, while the target group were fed a probiotic containing diet. Expression of certain target genes in liver and intestine were investigated by RNA isolation and cDNA synthesis following a real-time PCR.

Expression of three genes (il lb, tnfa, becn1) in liver in intestine which contribute to the innate immune system of zebrafish was measured. Il lb and tnfa are important cytokines in the innate immune response, while becn1 is a novel candidate gene of the innate immunity system.

In the intestine these genes of fish fed with the probiotic diet were upregulated. Gene expression in the liver showed no difference, except of becn1 which was downregulated. This is suggested to be caused by modulated lipid metabolism by inducing a decrease of the autophagic process in zebrafish. Additionally, expression of genes related to stress response on physiological and cellular levels, such as the expression of stress induced genes hsp70l and nr3cl were measured. Probiotic fed fish showed a decrease in the expression of these genes. Further, expression of genes (sod1, gpxl a, nos2a) which are related to oxidative stress response were evaluated. All genes showed a decrease in expression in treatments fed with the probiotic diet. Genes (tp53,casp3a) which are involved in apoptotic processes were also downregulated in the liver. 

All in all the study has shown that the probiotic L. rhamnosus has a positive impact on the innate fish immune system. Cytokines which play a key role in the immune response of zebrafish were upregulated and oxidative stress was reduced. The intestinal microbiota has been changed most likely by the effect of the probiotic.

This paper contributes promising results to the potential application of probiotics in e.g. aquaculture. Benefits of probiotics have been discussed extensively already. More research is needed in terms of technological difficulties, appropriate dosage and evaluation of the efficacy at the farm level. 

Gioacchini, Giorgia; Giorgini, Elisabetta; Olivotto, Ike u. a. (2014): „The Influence of Probiotics on Zebrafish Danio Rerio Innate Immunity and Hepatic Stress“. In: Zebrafish. 11 (2), S. 98-106, DOI: 10.1089/zeb.2013.0932.