甘草对大鲵抗嗜水气单胞菌感染的作用

通过投喂甘草提取物, 研究了甘草对大鲵(Andrias davidianus)抗嗜水气单胞菌(Aeromonas hydrophila)感染的作用。连续投喂56d, 从28d开始, 药物组血清溶菌酶活性先升后降, 呈抛物线趋势, 低剂量组在42d出现最大值(158.4±34.7) U/mL, 高剂量组在35d出现最大值(178.3±28.8) U/mL, 两者都显著高于同期对照组(P<0.05)。药物组在最后两次采样期, 即42d和56d时, 肾脏巨噬细胞吞噬活性显著高于对照组(P<0.05)。低剂量组和高剂量组最大值均出现在42d, 分别为(59.4±8.5)%和(58.4±5.2)%。同期相比, 药物组白细胞比容值均高于对照组。其中, 高剂量组在28d时白细胞比容值为(5.8±1.7)%, 低剂量组在56d时为(5.5±0.8)%, 高剂量组在56d时为(5.9±1.7)%, 三者都显著高于同期对照组(P<0.05)。药物组和对照组的脾脏脏器系数之间没有显示出显著差异。最后一次采样(56d)后人工感染嗜水气单胞菌, 对照组死亡率为90%, 低剂量组和高剂量组都为60%, 均低于对照组, 而药物组免疫保护率为33.3%, 也都高于对照组。结果表明, 投喂甘草提取物可在一定程度上提高大鲵对嗜水气单胞菌的抗性。

GLYCYRRHIZA URALENSIS ON ANTI-AEROMONAS HYDROPHILA INFECTION OF GIANT SALAMANDER (ANDRIAS DAVIDIANUS)

Chinese giant salamander (Andrias davidianus) is a national second-class key protected species. Wild giant salamanders mostly inhabit in mountain streams. They are widely distributed in Qinling Mountains of Shaanxi Province, China. There are three species of giant salamander namely Chinese giant salamander (A. davidianus), American giant salamander (Cryptobranchus alleganiensis) and Japanese giant salamander (A. japonicus). The septicemia of giant salamander caused by Aeromonas hydrophila is one of the common diseases. A. hydrophila is a common aquatic bacterium, which exists in natural water, but usually does not cause diseases. Only when the immunity of aquatic animals decreases, it is possible to infect the body through the digestive tract or skin wounds. Therefore, if it can enhance the activity of immune cells and immune molecules and improve its autoimmunity, it can effectively block the infection pathway of A. hydrophila and reduce the incidence of sepsis. Most of the used methods of Chinese herbal medicine in aquaculture are direct feeding of crude drugs, and there is no extraction and concentration of immunoactive components. Reports from the poultry industry believe that licorice has immunomodulatory effect on the body, but there is no report on the effect of licorice on the anti-disease ability of amphibian giant salamander. This study carried out this exploration after targeted extraction of the effective components of licorice.The effect of licorice on the anti-A. hydrophila infection of giant salamander was studied by feeding licorice extract to giant salamander. The results showed that from day 28 after continuous feeding, the serum lysozyme activity in the drug group increased firstly and then decreased, showing a parabolic trend. The maximum value was (158.4±34.7) U/mL in the low-dose group on day 42 and (178.3±28.8) U/mL in the high-dose group on day 35, both of which were significantly higher than those in the control group in the same period (P<0.05). The phagocytic activity of renal macrophages in the drug group was significantly higher than that in the control group at the last two sampling periods, i.e. 42d and 56d (P<0.05). The maximum values of low dose group and high dose group appeared at 42 days, which were (59.4±8.5)% and (58.4±5.2)% respectively. Compared with the same period, the leukocyte volume of the drug group was higher than that of the control group. Among them, the leukocyte specific volume of the high-dose group was (5.8±1.7)%, the low-dose group was (5.5±0.8)%, and the high-dose group was (5.9±1.7)%, which were significantly higher than those of the control group at the same time (P<0.05). There was no significant difference in spleen organ coefficient between the drug group and the control group. After the last sampling (56d), the mortality of the control group was 90%, and that of the low-dose group and the high-dose group were 60%, which were lower than that of the control group, while the immune protection rate of the drug group was 33.3%, which was also higher than that of the control group. The results showed that feeding licorice extract could improve the resistance of giant salamander to A. hydrophila to a certain extent.Chinese herbal medicine can indirectly affect the synthesis of protein by affecting the self replication of bacterial DNA and inhibiting its reproduction and growth, and finally inhibit the growth of bacteria. In terms of nonspecific immune defense function of the body, lysozyme, leukocytes and macrophages are extremely important immune molecules and immune cells. They can kill and effectively protect the body by dissolving or swallowing foreign pathogens. In this experiment, licorice improved the survival rate of giant salamander infected by A. hydrophila. At the same time, the activity of serum lysozyme, the number of leukocytes and the phagocytic activity of macrophages increased. Is there a correlation between them? Is the improvement of the survival rate of giant salamander caused by the improvement of these indicators, or is it caused by the fact that Chinese herbal medicine affects the synthesis of bacterial DNA and thus the synthesis of bacterial protein? Further research is needed.