| Antibiotic therapy leads to the rapid enhancement of antibiotic resistance of Salmonella bacteria,and the research and development speed of new antibiotics is far behind the speed of bacterial resistance,which seriously affects the high-quality development of aquaculture industry and public health safety.The research of antibiotic substitutes has been widely concerned,but the effect of phage therapy is not ideal.The development of phage products which can improve phage activity and bactericidal effect has become a hot topic.The purpose of this experiment is to study the phage microencapsulation technology,explore the stability and slow release performance of the phage microencapsulation and its therapeutic effect on Salmonella-infected chicks,and provide theoretical support for the phage therapy of bacterial diseases and the phage microencapsulation technology research.The results are as follows:1.Study on phage encapsulation technology of microencapsulated SP4.The cationic etherized starch,sodium alginate,xanthan gum,nano TiO2 CaCl2 and chitooligosaccharide were used as the raw materials for SP4 phage inclusion.The phage inclusion conditions were screened by orthogonal test and the phage microspheres were prepared.The results showed that when 2.4%cationic etherized starch,2%sodium alginate,0.5%xanthan gum,0.5%nano TiO2,2%CaCl2and 0.6%chito-oligosaccharide,the shape was regular,and the encapsulation rate was 97%.2.Study on biological characteristics of microencapsulated SP4 phage.The titer,pH stability,thermal stability,gastric fluid stability,intestinal fluid release process and preservation stability of microencapsulated SP4 phage were analyzed by conventional techniques.The results showed that the microencapsulated SP4 phage had high stability in the in vitro environment（pH5.0～9.0,10～30℃）.When pH2.0 and pH3.0 simulated gastric fluid conditions,the biological activity was higher at 0-30 min and 0-150 min,respectively.The simulated intestinal fluid was completely released after 4 h.There was no significant change in titer after 6 weeks at 4℃.3.Clinical effect of microencapsulated SP4 phage on salmonellosis infected chicks.A total of 75 1-day-old healthy chicks were randomly divided into 5 groups,which were negative control group,positive control group,phage treatment group and 2microencapsulated phage treatment groups.After Salmonella infection was treated with phage,the intestinal tract of chicks was collected and measured.The results showed that compared with the positive control group,the number of Salmonella colonized in ileum and colorectal of the control group was significantly decreased（P<0.05）,and the number of Salmonella colonized in duodenum,jejunum,ileum and colorectal of the microencapsulated phage treatment groupsⅠandⅡwas significantly decreased（P<0.05）.Compared with the phage treatment control group,the duodenum,jejunum and colorectal of groupⅠwere significantly decreased（P<0.05）,but the ileum had no significant change（P>0.05）.The number of Salmonella colonized in duodenum,jejunum,ileum and colorectal in groupⅡwas significantly decreased by phage treatment（P<0.05）.The results showed that microencapsulated phages were better than free phages in the treatment of Salmonella infection.In conclusion,the stability and slow release performance of microencapsulated phage were significantly improved,the number of Salmonella colonizing the intestinal tract of artificially infected chicks was significantly reduced,and the damage effect of Salmonella on the intestinal tract was inhibited,which laid a foundation for the development and utilization of phage. |
