| Different experiments were conducted in the present study to investigate the effect of various kinds molecular weight of chitosan on the bacteriostasis in vitro and its mechanism , immunity function , digestive and adsorption function.The principium results showed that the antibacterial ability of chitosan was preferably and different effect was as a result of different molecular weight.The lower the molecular weight was , the more significant the effect was. The bacteriostasis mechanism was that chitosan could adsorb and make the bacteria sink together . As a result their cell wall was dilapidation. So their reproduction were restrained and the growth of bacteria were affected. Chitosan could enhance the immune function and the digestive function. In addition ,chitosan had the fine function of adsorption and it could conspicuously reduce the content of cholesterol and sulphadimidine in eggs.Six kinds of chitosans'minimal inhibitory concentration(MIC) were conformed by using doubling dilution.The chitosan agar culture medium and diffusion disc were made according to MIC. The results showed that Escherichia coli,Staphylococcus aureus,P.multocida and S.gallinarum could be inhibited by 1#,3#,4#,6# chitosan with certain concentration.But 2#,5# chitosan had hardly obvious microbiostatic effects in tested concentration. The chitosan culture medium contain 1MIC of 1#,3#,4# and 6# could inhabit above four kinds of bacteria and the diffusion disc (1# and 3#) need eight times MIC.The eight times of 1#,3# MIC chitosan diffusion disc inhibitory effects to the four bacteria were significant.The microbiostatic effect of 3# chitosan was the most evident according to the result of above experiment.The mechanism of the bacteriostasis of 3# chitosan to Escherichia coli and Staphylococcus aureus were studied by using of electron microscope and light microscope.The results suggested that the number of the bacteria in the tube with chitosan was much little than that of the tube without chitosan.The bacteria were adhered to a whole body.By using of electron microscope we found that the interspace of the bacteria had been enlarged . The configuration of the organelle had been destroyed and concentrate. The function of the cell membrane was disordered.The effect of 3# chitosan on the immunity system and digestive system of roosters were studied.120 Hailanhe roosters of one-day were randomly assigned to each of the 4 dietary groups on average. Chickens of the trial groups were fed with 2 percent of 3#chitosan at 5 day-old age. The first and the third group were inoculated Escherichia coli;the second and the fourth were inoculated Staphylococcus aureus.The results showed that chitosan could sigificantly ruduce the mortality of the rooeters and alleviate the clinical symptoms. 100 one-day Hailanhe roosters were randomly divided into 2 groups at average. The treatment included 2% 3# chitosan and the control group. At 14d, 21d and 28d the antibody titer of NDV were determined and the relative weight (%BW) of thymus, spleen and bursa were estimated. The above organs and duodenum, jejunum ,ileum and calcium tonsil were made the microscopic section respectively to observe the growth of the lymph apparatus and the infection on digestive system. The results indicated that the difference of all the index mentioned above between trial group and control group had no significant at 14d. At 21d and 28d, the diffence of the index of thymus between two groups were not significant,however , the index of bursa and spleen and the level of antibody titer of NDV between the two groups were significant. The development of the immunity apparatus of the trial group was much better than the control group. The enteric epithelial cell of the trial group was integrity and the villi of the intestines developed well. Chitosan had no stimulence to the intestines. The effect of 3# chitosan on the immunity system and digestive system of swine were studied. 30 swine of 30-day weaning young were assigned to 0.1% 3#chitosan and the blank control group...
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