| Due to the immature immune and digestive system, suckling rabbits are easily infected with pathogenic bacteria, which results in higher mortality. Probiotic strains of lactic acid bacteria can effectively adjust the intestinal microecological balance, improve mucin expression, strengthen the mucous barrier function, and therefore play animportant role in preventing the intestinal disease. Moreover, the ability of adhering to the host mucuslayer and cells is the prerequisite of prolonged and stable colonization.In order to develop suitable probiotic strains of lactic acid bacteria for rabbit, we isolated and screened lactic acid bacteria with high adhering ability from suckling rabbits, and investigated their effects on performance, gut microbiota and mucin expression. The results were showed as follows:1. A total of 20 stains of lactic acid bacteria were isolatedfrom intestinal mucous of 5-,7-and 10-day suckling rabbits. Antimicrobial property against Escherichia coli K88 were evaluated for the all isolated strains as well as the three strains of Lactobacillus casei(L.a1, L.a2 and L.a3) previously isolated from intestinal mucous of suckling rabbits. Seven new isolated strains significantly inhibited the growth of E.cloi K88, and theywere respectively identified asLactobacillus brevis(L.b); Enterococcus faecium(named as E.f1, E.f2 and E.f3); Lactobacillus plantarum(named asL.p1, L.p2 and L.p3) by 16 S rRNA sequencing analysis. The highest antimicrobial activity was found in the three Lactobacillus casei strains(P<0.05), followed by L.p2 and L.p3.2. The tolerance to the different pH artificial gastric juice and bile salts concentration were evaluated for the seven new lactic acid bacteria strains and thethree Lactobacillus casei strains. And then the adhesion rates to small intestinal mucin, hydrophobicity and autoaggregation were measured for the ten strains to screen strains with high adhesion property. The results showed that there were no significant difference in tolerance to artificial gastric juice at the same pH value among different strains(P<0.05). Tolerance abilities of L.b strains to different bile salt concentrations were significantly higher than that of L.a and E.f strains(P<0.05). L.p1, L.p2,L.p3,L.a2,E.f1 and E.f3 showed higher tolerance ability than other strains in simulated gastric juice with pH 3.0(P<0.05). The viable counts of L.p1 and L.p2 were higher than others in 0.3% bile salt(P<0.05), and followed by L.a2. There were no significant difference in adhesion rate betweenL.a2 and L.p2(P>0.05), and adhesion rate of L.a2 and L.p2 were significantly higher than that of L.b and E.fstrains(P<0.05). L.p2, L.a3 and L.a2 had higher hydrophobicity, and their hydrophobicity was higher than that of L.b and E.fstrains(P<0.05). L.p2 and L.a2 showed the highest aggregation ability(P<0.05). The overall trend presented the correlation between hydrophobicity and the aggregation, hydrophobic and adhesion ability. In conclusion, L.p2 and L.a2 were considered as the finest when synthetically evaluated.3. Finally, we studied the effect of oral administration of lactic acid bacteria strains L.p2, L.a2 and L.p2+L.a2 with high adhesion abilityon growth performance, intestinal morphology, microbiota and mucin expression in suckling rabbits. Forty nursing rabbits of 5-day-old were randomly divided into 4 groups. During the course of whole experiment, the control(CON),L.p2,L.a2 and L.p2+L.a2 treatments wereorally administrated with normal saline,strain L.p2, strain L.a2 and mixed strains(L.p2:L.a2=1:1), respectively.The results showed that administration of L.p2+L.a2 significantly increased ADG at 8~13 days(P<0.05),villus height and the ratio of villus height and crypt depth injejunum and ileum(P<0.05). There was a significant increase of villus height and MUC1 and MUC2 mRNA relative expression injejunum and ileum for L.p2 treatment(P<0.05). MUC1 mRNA relative expression is also significantly improved injejunum after intake of L.a2(P<0.05). Although the goblet cell density in small intestine, ADG after feeding with solid food and the indexes of appendix and spleen had no obvious changes for all the experimental groups(P>0.05), the relative proportion of Escherichia coli injejunum and ileum was significantly reduced(P<0.05) and the relative proportion of Lactobacillus inileum wasmarkedly increased(P<0.05).Insummary, administration of strains L.p2 with high adhering abilitysignificantly increased the relative proportion of Lactobacillus inileum and jejunum, inhibited Escherichia coli proliferation, promoted the growth of villi and improved MUC1 and MUC2 mRNA expression in jejunum and ileum. Based on these results, it is reasonable that L.p2 has good probiotic properties both in vivo and in vitro, and is expected to be developed asa new probiotic for rabbit. |
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