甘草多糖对单核细胞增生性李斯特菌体内外生长的影响

目的：探讨甘草多糖对单核细胞增生性李斯特菌（Listeria monocytogenes，Lm）体内外生长的影响。方法：采用平板计数法和荧光显微镜、分光光度法及Bliss法分别分析甘草多糖对Lm生长速率和生物被膜形成的影响及计算细菌对小鼠半数致死量（median lethal dose，LD50）。观察低剂量（1 mg/kg）、中剂量（10 mg/kg）和高剂量（100 mg/kg）甘草多糖对感染100×LD50 Lm小鼠的保护力。小鼠感染0.01×LD50的Lm后1、7、14、21、28、35 d剖杀小鼠，检测脾脏、肝脏和肺脏中Lm分布的消长情况。结果：低质量浓度时（10、20、50 μg/mL），甘草多糖随着质量浓度增加对Lm标准菌株10403S生长速率和生物被膜形成的促进作用呈上升趋势；但高质量浓度时（100、200 μg/mL）这种促进作用逐渐降低。Lm口服感染小鼠的LD50为2.70×108 CFU。高剂量甘草多糖对于100×LD50的Lm感染可提供50%的保护力。0.01×LD50的Lm感染小鼠，随着甘草多糖质量浓度增加小鼠脾脏、肝脏和肺脏的细菌量逐渐减少。结论：低质量浓度甘草多糖在体外对Lm的生长具有促进作用，但随着质量浓度增高促进强度逐渐降低，而甘草多糖可以提高小鼠抵抗Lm感染的能力。

Effect of Glycyrrhiza Polysaccharide on the Growth of Listeria monocytogenes in Vitro and in Vivo

Objective: To investigate the effect of Glycyrrhiza polysaccharide on Listeria monocytogenes (Lm) in vitro and
in vivo. Methods: Colony counting method and fluorescence microscope/spectrophotometric method were used to evaluate
the effect of Glycyrrhiza polysaccharide on the growth and biofilm formation of Lm, respectively. The median lethal
dosage (LD50) was calculated by Bliss method. Protective efficacy against 100 × LD50 Lm was tested in mice administered
with Glycyrrhiza polysaccharide at high, middle and low doses. Mice infected with 0.01 × LD50 Lm were killed at 1,
7, 14, 21, 28 and 35 days for the detection of bacterial distribution in spleen, liver, and lung. Results: The promotion
effect of Glycyrrhiza polysaccharide on the growth and biofilm formation of Lm 10403S at low concentrations (10, 20 and
50 μg/mL) was observed in a concentration-dependent manner, whereas it was slightly reduced at high doses (100 and
200 μg/mL). LD50 of Lm was 2.70 × 108 CFU. A total of 50% mice infected with 100 × LD50 Lm could still be alive after
administration of Glycyrrhiza polysaccharide (100 mg/kg). Bacterial number in spleen, liver, and lung of the mice infected
with 0.01 × LD50 Lm was gradually decreased by increasing the dose of Glycyrrhiza polysaccharide. Conclusion: Glycyrrhiza
polysaccharide at low doses can promote the growth of Lm in vitro, but this effect gradually decreases with the increase in
drug concentration. Conclusively, Glycyrrhiza polysaccharide has a protective effect against Lm infection in mice in vivo.