A growing concern for the high consumption of antibiotics in aquaculture has initiated a search for alternative methods of disease control. Improved resistance against infectious diseases can be achieved by the use of probiotics. Probiotics are live microorganisms supplemented in food or feed which give beneficial effects on the intestinal microbial balance. In the present study a dry feed containing lactic acid bacteria (Camobacterium diver gens) isolated from Atlantic cod (Gadus morhua) intestines was given to cod fry. After three weeks of feeding the fry was exposed to a virulent strain of Vibrio anguillarum. The death rate was recorded during further three weeks of feeding with lactic acid bacteria supplemented feed. A certain improvement of disease resistance was obtained, and at the end of the experiment lactic acid bacteria dominated the intestinal flora in surviving fish given feed supplemented with lactic acid bacteria. No obvious growth inhibition of V. anguillarum was observed in an in vitro mixed culture of this bacterium and the C. divergens isolated from cod intestines.

An antibacterial V V11 kDa protein designated chlamysin was isolated from viscera of the marine bivalve Chlamys islandica. Chlamysin inhibited the growth of all Grampositive and Gram-negative bacteria tested. The isolated protein was highly efficient in hydrolyzing Micrococcus luteus cells only at low pH (4.5^6.2) and at low temperature (4^35³C). No significant loss of enzyme activity was observed after 30 days storage at room temperature or after heating to 70³C for 15 min, suggesting relatively high protein structure stability. Sequenceanalyzed fragments of the protein revealed data which guided the isolation of the cDNA gene, encoding a 137 amino acid chlamysin precursor in scallops. The deduced protein contains a high portion of cysteine, serine and histidine residues and has a predicted isoelectric point below 7. The chlamysin protein was found to have sequence homology to an isopeptidase and to a recently published bivalve lysozyme.z 1999 Federation of European Biochemical Societies.

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