AQUAVET, Laboratory of Aquatic Animal Diseases, Department of Veterinary Medicine, Federal University of Lavras, Lavras, MG 37200-000, Brazil.
Vet Microbiol. 2010 Jan 6;140(1-2):186-92. doi: 10.1016/j.vetmic.2009.07.025. Epub 2009 Aug 8.
Streptococcus agalactiae (Lancefield group B; GBS) is a pathogen that causes meningoencephalitis in fish, mastitis in cows, and neonatal sepsis in humans. The objective of this study was to characterize S. agalactiae isolated from fish (n=27), cows (n=9), and humans (n=10) using pulsed-field gel electrophoresis (PFGE) and to investigate the virulence of the identified strains in Nile tilapia (Oreochromis niloticus). The PFGE types were determined by dendogram analyses and the in vivo virulence was evaluated by experimental infection (using i.p. and immersion routes) of Nile tilapia. Among the fish strains, 5 different PFGE patterns were observed and 21 strains showed the same genetic pattern. In some farms two or three profiles occurred simultaneously. The bovine and human strains exhibited high genetic diversity and few relationships were established among S. agalactiae strains from the three host origins analyzed. Eight S. agalactiae strains from fish caused high mortality of Nile tilapia. Three bovine strains infected Nile tilapia (by i.p. route) and two of those strains caused clinical signs of meningoencephalitis. All human strains (n=5) infected Nile tilapia (by i.p. route) and meningoencephalitis was induced by one strain (by both i.p. and immersion routes). In conclusion, the analyzed strains from the three natural hosts did not show genetic relatedness, yet some of the bovine and human strains were able to infect fish and cause meningoencephalitis. We suggest that genetic linkage is not a prerequisite for S. agalactiae to cross the host-specific barrier.
无乳链球菌（Lancefield 组 B；GBS）是一种病原体，可引起鱼类脑膜炎、奶牛乳腺炎和人类新生儿败血症。本研究的目的是使用脉冲场凝胶电泳（PFGE）对从鱼类（n=27）、奶牛（n=9）和人类（n=10）分离的无乳链球菌进行特征分析，并研究鉴定菌株对尼罗罗非鱼（Oreochromis niloticus）的毒力。通过聚类分析确定 PFGE 型，通过尼罗罗非鱼的实验感染（腹腔注射和浸泡途径）评估体内毒力。在鱼类菌株中，观察到 5 种不同的 PFGE 模式，21 种菌株显示出相同的遗传模式。在一些养殖场中，同时出现两种或三种图谱。牛和人类菌株表现出高度的遗传多样性，在所分析的三个宿主来源的无乳链球菌菌株之间很少建立关系。8 株来自鱼类的无乳链球菌导致尼罗罗非鱼死亡率很高。3 株牛株感染尼罗罗非鱼（腹腔注射途径），其中 2 株引起脑膜炎的临床症状。所有 5 株人类菌株（n=5）均感染尼罗罗非鱼（腹腔注射途径），1 株引起脑膜炎（通过腹腔注射和浸泡途径）。总之，来自三个自然宿主的分析菌株没有表现出遗传相关性，但一些牛和人类菌株能够感染鱼类并引起脑膜炎。我们认为，遗传连锁不是无乳链球菌跨越宿主特异性屏障的先决条件。
