甘草多糖影响副猪嗜血杆菌生长的体内外实验研究

Effect of Glycyrrhiza polysaccharide on Haemophilus parasuis in vitro and in vivo

为研究甘草多糖对副猪嗜血杆菌在体内外生长的影响，本研究首先利用平板计数法和分光光度法分别分析甘草多糖在体外对副猪嗜血杆菌生长速度和生物被膜形成的影响。然后将100 LD50副猪嗜血杆菌感染小鼠，观察甘草多糖对小鼠的保护力。最后将0.01 LD50副猪嗜血杆菌感染小鼠，迫杀小鼠后检测副猪嗜血杆菌在脾脏、肝脏、肺脏和心血的分布情况。结果显示，在低浓度时（10 μg/mL、20 μg/mL和50 μg/mL），甘草多糖随着浓度的增加对副猪嗜血杆菌血清型12 （HS1075）的生长速度和生物被膜形成呈逐渐促进趋势，但高浓度时（100 μg/mL和200 μg/mL），生长速度与50 μg/mL相比并无明显区别，但仍显著高于空白对照组，而对副猪嗜血杆菌生物被膜的形成量与空白对照组相比差异无统计学意义。副猪嗜血杆菌口服感染小鼠的LD50为2.00×10^7 cfu。高剂量（100 mg/kg）甘草多糖对于100 LD50副猪嗜血杆菌感染可提供60 %的保护力。0.01 LD50副猪嗜血杆菌攻毒小鼠，随着甘草多糖浓度增加小鼠脾脏、肝脏、肺脏和心血的细菌量逐渐减少。结果表明，在体内甘草多糖可以提高小鼠抵抗副猪嗜血杆菌的感染，对甘草多糖的临床应用提供一定的参考。

To investigate the effect of Glycyrrhiza polysaccharide on Haemophilus parasuis both in vitro and in vivo, colony counting and spectrophotometric methods were used to test effect of G.polysaccharide on the growth and biofilm formation of H.parasuis in invtro; Then, the protection efficacy against H.parasuis was tested in mice with G.polysaccharide at different doses. The bacteria distribution was detected in samples of spleen, liver, lung, and heart blood collected from the mice at different days post infection with 0.01 LD50 of H.parasuis. The results indicated that the effect of G.polysaccharide was able to promotion on the growth and biofilm formation of H.parasuis serovar 12 （HS1075） at lower concentration （10 μg/mL, 20 μg/mL and 50 μg/mL） in vitro, and in a concentration-dependent manner. However, there was no significant difference in biofilm formation of H.parasuis between the high doses （100 μg/mL and 200 μg/mL） group and the control group. In addition, 60% mice infected with 100 LD50 （2×10^9 cfu） H.parasuis survived after administration of high doses of G.polysaccharide （100 mg/kg）. While, the bacterial number in spleen, liver, lung, and heart blood of the mice infected with 0.01 LD50 H.parasuis decreased gradually along with the treatment of G.polysaccharide. The results showed that G.polysaccharide was able to promote the growth of H.parasuis at low doses in vitro. However, G.polysaccharide improved the protection effect against H.parasuis infection in mice in vivo.