Characterization of probiotic properties of lactic acid bacteria isolated from an estuarine environment for application in rainbow trout (Oncorhynchus mykiss, Walbaum) farming

Abstract

Bacterial attachment to fish surfaces and the capacity to compete with pathogens for adhesions sites are essentials characteristics in order to select a candidate probiotic for aquaculture of rainbow trout. Twelve lactic acid bacteria (LAB) isolated from fish and sediments from Bahía Blanca Estuary, Argentina, were examined for in vitro adhesion to rainbow trout mucus, cell surface properties and competitive exclusion against two salmonid pathogens: Yersinia ruckeri and Aeromonas salmonicida. In order to assess their survival through the digestive tract pH and rainbow trout bile tolerances were evaluated.All LAB strains survived for 1.5 h of incubation in 10 % rainbow trout bile. Most of the strains survive 1.5 h at pH 3.0, and three of them showed a reduction of viable counts lower than 2 logarithms, with respect to control (pH 6.5). Only a few strains showed tolerate pH 2.0. All the strains were able to attach to rainbow trout skin mucus (104-106 cells/cm2), to glass (104-105 cells/cm2) and to stainless steel (103-104 cell/cm2). Sixty percent of LAB strains were capable of competing and exclude successfully Y. ruckeri and all strains were able to displace it. Against A. salmonicida, 75 % of LAB strains compete successfully, 50 % were capable of displacing and 60 % exclude it. Our data suggest a potential of these strains as anti-infective agents in the rainbow trout culture. This study is the first report on probiotic perspective of LAB strains isolated from an estuarine environment from Argentina.