| Antibiotics have been widely used as growth promoter in animal husbandry since 1950s. The overuse of antibiotics results in the rapid evolution of pathogenic bacteria with resistance to drugs, which would indirectly do harm to the public health. Moreover, the antibiotics growth promoters (AGP) deposited in livestock products can affect the human health directly. The usage of AGP has been oppugned. In order to decrease the use of AGP and overcome antibiotic resistance, it is very important and urgent to prepare and develop safe antibacterial agents that can substitute antibiotics.In the present study, natural aminopolysaccharide was selected as the based material to prepare aminopolysaccharide nanoparticles by nanotechnology. The characteristics and adsorption properties was studied. Then, aminopolysaccharide nanoparticles loaded with different metal ions were constructed. In order to selected materials with high bactericide, their main characteristics and antibacterial activities against E.coli and S.aureus were determined in vitro. Aminopolysaccharide nanoparticles loaded copper ions (APN) showed high antibacterial activities and was selected to further study. APN was orally administrated to rat to evaluate its effect in vivo.The main results were listed as follow:1. Aminopolysaccharide nanoparticles were regular spheres with a mean diameter of 53.99 nm in a narrow size distribution and a Zeta potential of+51.37mV. It belongs to zero-dimension nano-material, namely, nanoparticles. The nanoparticles showed a high adsorption capacity for eosin Y which was found to be 3.333g/g. The experimental data followed Langmuir isotherm model.2. Compared to the aminopolysaccharide nanoparticles, both the mean diameter and the Zeta potential increased when different metal ions were loaded. The antibacterial activity was direct proportional to Zeta potential. The results obtained from antibacterial trial in vitro indicated that aminopolysaccharide nanoparticles loaded Ag+showed the highest antibacterial activity against E.coli and S.aureus, with a minimal bactericide of 6μg/ml and 12μg/ml, respectively. The order of the other four kind materials were aminopolysaccharide nanoparticles loaded Cu2+, aminopolysaccharide nanoparticles loaded Zn2+, aminopolysaccharide nanoparticles loaded Mn2+, aminopolysaccharide nanoparticles loaded Fe2+, which were 12μg/ml and 24μg/ml,24μg/ml and 48μg/ml,97μg/ml and 97μg/ml,195μg/ml and 195μg/ml, respectively. The antibacterial activity of aminopolysaccharide nanoparticles loaded Fe2+ was almost the same with that of aminopolysaccharide nanoparticles (187μg/ml and 281μg/ml).3. APN were regular spheres with a mean diameter of 121.90 nm in a narrow size distribution and a Zeta potential of+88.69mV. The results obtained from antibacterial trial in vitro indicated that the MBC of APN against E.coli K88 and S.chloraesuis was 12μg/ml. The morphological changes of E.coli K88 during treated by APN under AFM showed that the bacterial membrane was destroyed, and holes of various sizes appeared on the cell surface. So it was supposed that membrane probably the active site of APN. Membrane damage and release of content of bacterial cell may be the main mechanism of the killing process.4. Male SD rats (average body weight of 85±2 g) were used in feeding trial. APN was orally administrated to rats at dosage of 80 mg/kg b.w. and 160 mg/kg b.w. for 21 days. Compared with the control group, ADG and FER were enhanced by APN with 8.5%(P＜0.05) and 14.1%(P＜0.05),17.2%(P＜0.05) and 22.5%(P＜0.05), respectively. The total protein in the serum increased by 17.2%(P＜0.05) and 22.5 %(P＜0.05), while urea nitrogen in the serum decreased by 41.0%(P＜0.05) and 52.3%(P＜0.05), respectively. The concentration of IgA and IgG increased by 32.9 %(P＜0.01) and 39.7%(P＜0.01),64.1%(P＜0.01) and 108.9%(P＜0.01), respectively. The concentration of C3 increased by 31.7%(P＜0.05) and 48.8% (P＜0.05). The activity of lysosome were 5.3 fold (P＜0.01) and 6.0 fold (P＜0.01) higher than that of the control group. The lymophocytes transformation rate of the peripheral blood and spleen induced by Con A and LPS were enhanced by 8.8% (P＜0.05) and 23.4%(P＜0.05),2.8%(P＜0.05) and 21.1%(P＜0.05). The results of the immune parameter suggested that APN improved the immune function of the rats.5. Further study showed that APN modulate the composition of the microbiota of the caecum in rats. Compared to the control group, the lact and biofidobacteria were significantly enhanced, whereas, the total anaerobe, total aerobe, coliform, Salmonella and C.perfringens were significantly lowered,α-galactosidase,β-galactosidaseandα-glucosidase (P＜0.05) were significantly enhanced, which suggested that the microbial digestion was improved. On the contrary, the activity ofβ-glucuronidase was significantly lowered, indicating that the pathogenic bacteria decreased. The concentrations of propionate and butyrate were enhanced, and the pH of the caecum digesta was lowered, significantly. The morphology and structure of the small intestine were apparently improved by APN, which was characterized with longer mivrovillus and shallower crypt depth. Meanwhile, the activity of disaccharidase (sucrase, maltase and lactase) was significantly enhanced. Besides, the trypsin, lipase and amylase of the intestinal digesta also significantly increased by 17.26%(P＜0.05) and 25.34%(P<0.05),33.04%(P＜0.05) and 59.06% (P＜0.05),32.65%(P<0.05) and 45.92%(P＜0.05), respectively.
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