Isolation of putative probionts from cod rearing environment H.L. Lauzon a,b, * , S. Gudmundsdottir c , M.H. Pedersen d,1 , B.B. Budde d , B.K. Gudmundsdottir c a Matis, Icelandic Food Research, Skulagata 4, 101-Reykjavik, Iceland b University of Iceland, Department of Medicine, Vatnsmyrarvegur 16, 101-Reykjavik, Iceland c Institute for Experimental Pathology, University of Iceland, Keldur, Vesturlandsvegur, 112-Reykjavik, Iceland d University of Copenhagen, Department of Food Science, Faculty of Life Sciences, Rolighedsvej 30, 1958 Frederiksberg C, Denmark Received 11 April 2008; received in revised form 6 May 2008; accepted 9 May 2008 Abstract Survival problems are encountered at early stages of intensive fish rearing and antibiotics are widely used to remedy the situation. Probiotics may provide a potential alternative method to protect larvae from opportunistic and pathogenic bacteria and promote a balanced environment. This study was designed to search for new probiotics to target this critical period in cod rearing. Potential probionts were selected from the natural microbiota of cod aquacultural environment. The selection was based on several criteria: pathogen inhibition potential, growth characteristics, strain identification, metabolite production and adhesion to fish cell lines. Our study demonstrated that 14% of screened bacteria (n = 188) had antagonistic properties towards fish pathogens. The majority of these isolates were Gram-positive (81%), belonging to Firmicutes (69.2%) and Actinobacteria (11.5%) phyla based on 16S rRNA gene sequencing. Only 6 (3.2%) of 188 isolates could inhibit all three pathogens tested: Vibrio anguillarum, Aeromonas salmonicida subsp. achromogenes and Vibrio salmonicida. Differences observed in activity intensity and spectrum among inhibitory isolates emphasise the need to develop probiotic mixtures for efficient prophylactic methods. Comparison of growth behaviour of inhibitory isolates and pathogens at cod rearing temperatures, metabolite production and adhesion capacity were considered for final probiont selection. Four promising isolates that could be used as a mixed supplement to rearing water were identified as putative probiotic bacteria. This study emphasises the importance and potential of lactic acid bacteria in aquaculture. # 2008 Elsevier B.V. All rights reserved. Keywords: Cod aquaculture; Probiotic; Fish pathogens; Antagonism; Growth characteristics; Adhesion 1. Introduction Proliferation of opportunistic and pathogenic microorganisms in intensive rearing systems is known to cause poor larval growth and high mortality rates (Munro et al., 1995). Antibiotics have been used to prevent and control bacterial www.elsevier.com/locate/vetmic Available online at www.sciencedirect.com Veterinary Microbiology 132 (2008) 328–339 * Corresponding author at: Matis, Icelandic Food Research, Sku- lagata 4, 101-Reykjavik, Iceland. Tel.: +354 4225061; fax: +354 4225001. E-mail addresses: helene.l.lauzon@matis.is (H.L. Lauzon), siggag@hi.is (S. Gudmundsdottir), mhp@cook.wce.com (M.H. Pedersen), bjarngud@hi.is (B.K. Gudmundsdottir). 1 Present address: William Cook Europe ApS, Sandet 6, 4632 Bjaeverskov, Denmark. 0378-1135/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.vetmic.2008.05.014