水産養殖研究開発ジャーナル

概要

An ex vivo approach to studying the interactions of Pediococcus acidilactici and Vibrio (Listonella) anguillarum in the anterior intestine of rainbow trout Oncorhynchus mykiss

Glenn M. Harper, Matthias Monfort, Imad P. Saoud, Matthew J. Emery, Sanaa Mustafa, Mark D. Rawling, Ben Eynon, Simon J. Davies and Daniel L. Merrifield

The aim of the present study was to observe the antagonistic relationship of the probiotic Pediococcus acidilactici and the pathogen Vibrio (Listonella) anguillarum in the intestine of rainbow trout (Oncorhynchus mykiss) by using the ex vivo intestinal sac method. Rainbow trout (240-250g) were fed either a control diet (commercial diet: 43% protein, 20% lipid) or a probiotic diet (control diet supplemented with P. acidilactici [Bactocell] at log 7 CFU g-1) for two weeks. The anterior intestine was then isolated for an ex vivo challenge study and intestinal sacs formed by shutting one end of the intestinal portion. The sacs were filled with PBS solutions containing either no bacteria (as a control), the probiotic (P. acidilactici), the pathogen V. anguillarum, or probiotic+pathogen and incubated for one hour. At the end of the exposure bacterial levels in the lumen were determined by culture based approaches and colonisation of the mucosa assessed with PCR-DGGE and electron microscopy (EM). Intestinal morphology (observation of gross morphological damage, ultrstructural differences and the quantification of goblet cells and intra epithelial lecuocyte numbers) and bacterial infection/translocation was assessed using light microscopy (LM) and EM. Results revealed that V. anguillarum caused extensive histological damage to the gut but P. acidilactici did not. No signs of translocation of either the probiotic or pathogen were observed. Microbiological analyses indicated that P. acidilactici was able to outcompete V. anguillarum in the rainbow trout intestine and also to populate or colonise the mucosa. Additionally, elevated leucocyte levels and goblet cells in the epithelium of P. acidilactici fed fish, and intestines exposed to P. acidilactici, suggests that P. acidilactici might have potential use in controlling vibriosis. In vivo disease-challenge studies are warranted to ascertain if V. anguillarum infections can be controlled in rainbow trout using dietary applications of P. acidilactici.