Ex-vivo test of probiotics and vibriosis in the GI tract of fish

The gastrointestinal tract is an important mode of entry for pathogens in fish, with one of the main problems being the cause of vibriosis. The use of probiotics have been shown to protect against such disease via the fortification of the intestinal microbiota, improving the immune system or permitting pathogenic bacteria to be outcompeted. However these studies have involved in-vitro methods and therefore do give a true representation of the probiotic-pathogen interaction in the gastrointestinal tract of fish. The study by Harper et al. (2011) aimed to investigate the relationship between the probiotic Pediococcus acidilactici and the pathogen Vibrio (Listonella) anguillarium in rainbow trout intestines using an ex-vivo method.

Fish were obtained from a fish farm in the UK and, after four weeks of an ab libitum diet, distributed in six tanks with 20 fish each. These were then divided with one group being fed a controlled diet and the other group the same diet supplemented with Pediococcus acidilactici for two weeks, with three replicates of each. The anterior intestine was then removed and one end tied off to create an intestinal sac. These were filled with a PBS solution and either no bacteria, the probiotic, the pathogen or both the probiotic and the pathogen and incubated for one hour. PR-DGGE was used to analyse the colonisation of bacteria in the lumen and mucus and electron microscopy to establish any morphological damage or ultrastructure differences to the intestine and any bacterial colonisation or translocation.

The probiotic caused no damage to the intestine, however the pathogen was found to cause much histological damage. Translocation was not observed in either sample. The probiotic was observed to out-compete the pathogen in both the intestine and the mucosa. This was thought to be related to the observed increase in leucocyte cells and goblet cells in the epithelium both when given the probiotic diet or when simply exposed to the probiotic. Such protection of the epithelial tissue therefore may enable the prevention of vibriosis.

These findings are important in improving the understanding of the probiotic-pathogen host interactions and the benefits that a probiotic supplemented diet could have on the disease resistance in the gastrointestinal tract of fish. The use of ex-vivo experiments enabled this theory to be confirmed without the need to use a large quantity of animals, but further studies using in-vivo methods would now be required to determine the potential of commercially using probiotics for disease resistance in fish.

Harper, G.M., Monfort, M., Saoud, I.P., Emery, M.J., Mustafa, S., Rawling, M.D., Eynon, B., Davies, S.J. and Merrifield, D.L. (2011) An ex vivo approach to studying the interactions of Pediococcus acidilactici and Vibrio (Listonella) anguillarum in the anterior intestine of rainbow trout Oncorhynchus mykiss. Aquaculture Research and Development. Available online at:

http://www.omicsonline.org/2155-9546/2155-9546-S1-004.digital/2155-9546-S1-004.html