无乳链球菌不同途径感染吉富罗非鱼后病原菌在体内的分布规律研究

为探讨无乳链球菌(Streptococcus agalactiae)感染罗非鱼(Oreochromis spp)的致病途径。采用腹腔注射、灌胃和浸泡三种方式对吉富罗非鱼进行无乳链球菌(HN016菌株)胁迫感染,利用平板活菌计数法统计三种方式感染后病原菌在体内组织的分布。注射和灌胃两种方式感染后均出现典型的链球菌感染发病症状,其中注射组在感染24 h后出现死亡高峰,死亡率为92.5%;灌胃组感染48 h后出现死亡高峰,死亡率为90%;而浸泡组,感染后均没有出现明显的发病症状,也没有出现死鱼。注射组和灌胃组在感染后2 h,其脾脏、肝脏、前肾、胃、腮、皮肤和肌肉组织中均可分离出病原菌,5 h后在脑组织中均可分离出病原菌,8 h后各组织分离出的病原菌数达到峰值;而浸泡组在感染8 h后才从各组织中分离出病原菌,且它们的数量均低于同时期的注射组和灌胃组。注射和灌胃两种方式可使吉富罗非鱼快速感染无乳链球菌而发病,而浸泡方式感染后病原菌虽可以侵入机体,但不表现出症状。由此,我们推测在自然条件下养殖的罗非鱼是通过口腔采食携带无乳,链球菌的食物而被感染。

The distribution pattern for pathogenic bacteria of Streptococcus agalactiae infect Oreochromis niloticus in vivo by different ways

In recent years, Streptococcus agalactiae has become one of the most serious bacterial disease in China , but the pathogenic of S.agalactiae to tilapia is still unknowed.Oreochromis niloticus was infected to S.agalactiae ( HN016 strain) by injection, gavage and soak in this study to investigate the pathogenic pathway, the clinical signs of each group were recorded after infection.The number and distribution of the pathogenic bacteria were recorded by the tablet count meth-od.The results showed that the typical symptoms of S.agalactiae infection disease were observed in both injection and ga-vage groups, but no symptoms and dead fish were observed in soak group.The peak time of death were appeared in 24 h and 48 h for injection and gavage groups, respectively.Moreover, the mortality rates for these two groups were 92.5% and 90% , respectively.In terms of pathogen separation, the pathogenic bacteria could be isolated from spleen, liver, kidney, stomach, gill, skin and muscle tissues after 2 h infection, the brain was detected after 5 h infection.The concentration of pathogenic bacteria was isolated from injection and lavage group after 8 h infection.Pathogenic bacteria in soak group was less than injection and lavage groups at the same periods.O.niloticus was quickly infected and dead after injection and lav- age infection, and the pathogen could also invade in vivo after high concentration soak infection.However, no disease symptoms and death in soak infection.We suggested that in natural conditions tilapia was infected by picking up food from the mouth, which was carried by S.agalactiae.