Gilthead seabream (Sparus aurata L.) innate immune response after dietary administration of heat-inactivated potential probiotics Patricia Dı´az-Rosales a , Irene Salinas b , Alejandro Rodrı´guez b , Alberto Cuesta b , Mariana Chabrillo´n a , M. Carmen Balebona a , M. A ´ ngel Morin˜igo a , M. A ´ ngeles Esteban b, * , Jose´ Meseguer b a Department of Microbiology, Faculty of Sciences, University of Ma ´laga, 29071 Ma ´laga, Spain b Fish Innate Immune System Group, Department of Cell Biology, Faculty of Biology, University of Murcia, 30100 Murcia, Spain Received 27 April 2005; accepted 21 June 2005 Available online 5 October 2005 Abstract The effects of the dietary administration of two heat-inactivated whole bacteria from the Vibrionaceae family, singly or combined, on innate immune response of the seabream were studied. The two bacteria (Pdp11 and 51M6), which were obtained from the skin of gilthead seabream, showed in vitro characteristics that suggested they could be considered as potential fish probiotics. The fish were fed four different diets: control (non-supplemented), or diets supplemented with heat-inactivated bacteria at 10 8 cfu g ÿ1 Pdp11, 10 8 cfu g ÿ1 51M6 or with 0.5 ! 10 8 cfu g ÿ1 Pdp11 plus 0.5 ! 10 8 cfu g ÿ1 51M6 for 4 weeks. Six fish were sampled at weeks 1, 2, 3 and 4, when the main humoral (natural haemolytic complement activity and serum peroxidase content) and cellular innate immune responses (leucocyte peroxidase content, phagocytosis, respiratory burst and cytotoxicity) were evaluated. The serum peroxidase content and the natural haemolytic complement activity increased with time, reaching the highest values in the third and fourth weeks of feeding, respectively. The phagocytic ability of specimens fed the mixture of the two inactivated bacteria was significantly higher than in the controls after 2 and 3 weeks of treatment. The same activity increased significantly in seabream fed the Pdp11 diet for 2 weeks or the 51M6 diet for 3 weeks. Respiratory burst activity was unaffected by all the experimental diets at all times assayed. Cytotoxic activity had significantly increased after 3 weeks in fish fed the 51M6 diet. These results are discussed in terms of the usefulness of incorporating inactivated probiotic bacteria into fish diets. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Probiotics; Vibrionaceae; Innate immunity; Leucocytes; Gilthead seabream (Sparus aurata L.); Teleosts * Corresponding author. Tel.: C34 968363963; fax: C34 968363965. E-mail address: aesteban@um.es (M.A ´ . Esteban). 1050-4648/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.fsi.2005.06.007 Fish & Shellfish Immunology 20 (2006) 482e492 www.elsevier.com/locate/fsi