Changes in intestinal microbiota and humoral immune response following probiotic administration in brown trout (Salmo trutta)

Abstract

We studied the effect of several lactic acid bacteria (LAB) on the humoral response of brown trout (Salmo trutta). LAB groups (Lactococcus(Lc.)lactisssp.lactis,Lactobacillus(Lb.)sakeiandLeuconostoc(Leu.)mesenteroides) were administered orally at 106colony-forming units/g feed to brown trout for 2 weeks, after which fish were switched to an unsupplemented feed. Blood and intestinal samples were taken from the onset of feeding supplemented diets at 1, 2, 3 and 4 weeks. During the LAB-feeding period,Lc. lactisssp.lactis,Lb. sakeiandLeu. mesenteroidespersisted in the fish intestines, but the number of LAB slowly decreased in the intestines after changing to the unsupplemented diet. OnlyLb. lactisssp.lactisandLeu. mesenteroideswere detected at levels above 1 × 102colony-forming units/g at the end of the fourth week. In comparison to untreated control fish, the alternative complement activity in the serum was found to be significantly greater in all LAB groups at the end of the second week. Groups supplemented withLc. lactisssp.lactisandLeu. mesenteroidesexhibited an elevated level of lysozyme activity at the end of the third week, but the group supplemented withLb. sakeidid not exhibit any significant change in lysozyme activity. Serum immunoglobulin levels were higher compared with the control group, but there was no significant difference between the LAB and control groups.