| Lactic acid bacteria (LAB) were a class of beneficial bacteria which couldproduce lactic acid and recognized as the safe probiotics. The LAB could improvethe host health through affecting intestinal flora and the nonspecific immunity toincrease the ability of disease resistance.In this experiment, a strain of lactic acid bacteria, Leuconostoc lactis, wasisolated from the intestinal tract of black porgy, Sparus macrocephalus, andidentified by conventional biochemical characteristics and16S rDNA gene sequenceanalysis. Then the aim of the study was to characterize the probiotic properties of theisolated strain in vitro. The isolated strain had the ability of bile tolerance andresistance to low pH, and could survive well in the trypsinase and pepsin solution.But the high concentration of two enzymes could affect its viability. The isolate wassensitive to most of common antibiotics that were tested in experiment, and it wasresistant to several antibiotics, including Cephalothin, Ceftriaxone, Imipenem andTobramycin. The isolate could autoaggregate itself and coaggregate with otherbacteria in intro. The autoaggregation percentage could increase to23.29%after20hof incubation. The percentage of coaggregation were respectively10.74%,24.36%,16.49%,24.41%,20.99%,29.44%and31.21%for Escherichia coli O157, Shigella,Salmonella typhimurium, Staphylococcus aureus, Proteusbacillus vulgaris, Listeriamonocytogenes and Vibrio parahaemolyticus after20h incubation of a mixedsuspension. In addition, the isolated strain also has broad spectrum bacteriostasisactivities. The supernatant of the strain could inhibit the growth of E. coli O157, S.typhimurium, P. vulgaris, V. parahaemolyticus, Vibrio harveyi, Vibrio alginolyticus,Bacillus subtilis, Shigella and S. aureus, especially, inhibit the growth of E. coliO157, S. typhimurium, P. vulgaris and Vibrio best.48healthy juvenile fishes about50g were randomly divided into control group,lysozyme group and Leuconostoc lactis experimental group. The fishes in lysozymegroup and Leuconostoc lactis experimental group were respectively administered with feed containing recombinant lysozyme (7200U/g) and1×10~7cfu/g Leuconostoclactis for56days. The fishes were slaughtered to get the samples of blood serum,intestine and intestinal content at the14d,28d,42d and56d. The glucose and proteincontent, SOD and lysozyme vitality in the serum and serum antibacterial vitalitywere tested to evalute the serum biochemical indicators. The intestinal cross-sectionpictures were made and dyed through HE method to survey the morphology. Themicroflora of intestinal wall and content were analyzed by PCR-DGGE technology.The results showed that: The similarity of microflora composition in the intestinalwall according to UPGAMA analysis were0.52、0.45、0.66、0.7and that in theintestinal contents were0.57、0.61、0.66、0.69at14d,28d,42d,56d. The bands ofLeuconostoc lactis experimental group in DGGE fingerprints of microflora in theintestinal wall weresignificantly higher (P<0.05) than the control group andlysozyme group at14d,28d,42d,56d. The bands of Leuconostoc lactis experimentalgroup in DGGE fingerprints of microflora in the intestinal contents weresignificantly higher (P<0.05) than the control group and lysozyme group at56d, andwere not significantly different between the three groups. The results indicated thatLeuconostoc lactis could raise the intestinal microflora diversity to a certain extent.The dominant bacteria in intestine of juvenile fishes were Pseudomonadaceae,Enterobacteriaceae, Micrococcaceae, Rhodobacteraceae, Acinetobacter,Exiguobacterium and Brevibacterium according to the same positioned bands ofthree groups were collected and sequencing. The muscularis, mucosa and villi of theintestine were physically better developed for the juvenile fish in the Leuconostoclactis experimental group during the periods. The intestinal muscularis thicknesses ofthe fish were not significantly different between the three groups during the periods.The intestinal mucosal thickness of the fishes in the experimental group wassignificantly higher than the control group (P<0.05) at14d,28d,42d,56d, andsignificantly higher than the lysozyme group at14d,28d. The intestinal villi widthsof the fish were not significantly different between the three groups during theperiods. The villi length of the fishes in the experimental group was significantlyhigher than the control group (P<0.05) at14d,28d,42d,56d, and significantly higherthan the lysozyme group at14d,28d,42d. Therefore, the Leuconostoc lactis in feedcould improve the intestinal morphology of Sparus macrocephalus juvenile fish The serum glucose content of juvenile fishes in the experimental group and lysozymegroup were significantly lower than the control group (P<0.05) at56d, but was notsignificantly different with lysozyme group. The serum protein content of juvenilefishes in the experimental group was significantly higher than the control group andlysozyme group (P<0.05) at42d. The serum SOD vitality of the fishes in theexperimental group was significantly higher than the control group (P<0.05) at56d,but was not significantly different with lysozyme group. The serum lysozyme vitalityof the fishes in the experimental group was significantly higher than the controlgroup (P<0.05) at42d,56d, and significantly higher than the lysozyme group at42d.The serum antibacterial vitality of the fishes in the experimental group wassignificantly higher than the control group (P<0.05) at42d,56d, but was notsignificantly different with lysozyme group. Consequently, the Leuconostoc lactis infeed could improve serum biochemical indicators of Sparus macrocephalus juvenilefish to a certain extent... |
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