| Probiotic is an ideal substitute of antibiotic. Free of medicaments and contamination,it can improve animal's growth performance,boost immunity and has been widely used in the breeding industry. Recent researches showed that some new bacteria had distinct probiotic properties except for the directory of microbe feed additives issued by the Ministry of Agriculture. This experiment is intended to screen out yak enterococcus hirae with bacteriostatic ability and study its effect on the mouse's growth and intestinal mucosal immunity in order to lay a theoretical basis for preparation of yak probiotics. Major achievements are as follows:1. Screening, identification of yak enterococcus hirae, and preliminary study on its partial biological characteristics.85 trains of yak lactic acid bacteria were cultured in a Carbon dioxide incubator by37 ? for 28 h with MRS, centrifuged supernatant was obtained. Then we adjusted p H value to 5.5 and measured the bacteriostatic ability against salmonella indicator. 9 strains of lactic acid bacteria with bacteriostatic ability were selected,which the diameter of inhibition zone was larger than 12 mm. We amplified 16 s r RNA gene sequence of the 9 strains and identified 5 strains of enterococcus hirae. Finally, the strain Swun3 with the strongest resistant ability was screened out by acid and bile salt tolerance test and susceptibility test.And we studied its partial biological characteristics.The results showed that the survival rate was 61.9% under p H=3, the survival rate was 27.8% when the salting strength was0.3%. The maximum growth inhibition zone(GIZ) was 16 mm against Shiga-Toxigenic Escherichia coli and Salmonella clinical isolates. According to the Swun3's growth tendency, the logarithmic phase of growth was 2-27 h, the concentration of viable bacteria could reach 5.4×1010 CFU/m L before the platform period and the cultural supernatant(37?,30h) had the strongest bacteriostatic ability. The strain Swun3 was sensitive to commonly used antibiotics. In conclution, yak enterococcus hirae Swun3 had a strong resistance against Salmonella and Escherichia coli as well as a strong tolerance to gastrointestinal tract condition, and no drug resistance. It was an excellent yak enterococcus hirae with bacteriostatic ability.2. The influence of yak enterococcus hirae Swun3 on mice's growth performance and intestinal mucosal immunity.28 female Kunming mouse weighed about 20 g were divided into 4 groups. The mice of group 1-3(experimental groups) were gavaged with 0.5m L Swun3 of different concentration of 106 CFU/m L, 107CFU/m L and 108 CFU/m L. And 0.5m L MRS was gavaged to the mice of group 4(control group). The 4 groups were gavaged for 21 days,and feed intake was weighed everday. On the 14 th day, 3 mice of each group were collected eyeball blood, viscera, and intestinal mucosa. The remaining 4 of each group were treated in the same way on the 7th day after gavage. The results showed as below: on the 7th day, the feed gain ratio of the mice gavaged with the concentration of 108CFU/m L was obviously less than the control group(P<0.05). On the 7th day after gavage, the average level of SIg A was significantly higher(P<0.05). The blood biochemical index of the 4 groups were proved to be normal and the visceral index had no significant difference between experimental groups and control group. In conclusion, yak enterococcus hirae Swun3 can facilitate mouce's growth performance and improve intestinal mucosal immunity, so it can be used as a candidate of yak probiotics. |
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