Analysis on pathogenic mechanism of fish pathogen Edwardsiella tarda

(1)迟发爱德华菌在小鼠巨噬细胞内的细胞内复制依赖于ⅲ型分泌系统，迟发爱德华菌是一种宿主范围广泛的病原体，可以感染动物和人类。这种细菌的致病性可能与抗吞噬作用有关。研究结果表明，小鼠巨噬细胞内延迟棘球绦虫的细胞内复制依赖于III型分泌系统，并通过上调抗凋亡NF-kappaB靶基因诱导抗凋亡作用。野生型菌株在巨噬细胞吞噬体膜内复制；而III型突变体则没有。(2)微阵列分析微阵列分析显示，与感染III型突变体的巨噬细胞相比，感染野生型菌株的巨噬细胞中NF-kappaB靶基因（如促炎因子和抗凋亡基因）的mRNA表达水平上调。抗凋亡的NF-kappaB靶基因的上调是延迟e.a的抗凋亡活性增强的原因，也是小鼠巨噬细胞胞内复制所必需的(3)III型分泌系统依赖的NF-kappaB激活对延迟爱德华菌在人上皮细胞内生长的抑制。接下来，我们发现TTSS在人上皮细胞内生长也需要TTSS （Hep-2）。然而，与先前对小鼠巨噬细胞的微阵列分析不同，在感染的Hep-2细胞中未检测到NF-kappaB靶基因mRNA表达水平上调。在NF-kappaB报告基因试验中，野生型E - tarda，而不是其TTSS突变体，实际上抑制了肿瘤坏死因子α依赖性NF-kappaB的激活。这些结果提示ttss依赖性地抑制了迟发E.感染Hep-2细胞的NF-kappaB活化。综上所述，这些结果表明，专门针对该细菌III型分泌系统的药物或疫苗可能有助于减少由该细菌感染对养殖鱼类（如红鲷鱼和日本比目鱼）造成的工业损失。少

(1) Intracellular replication of Edwardsiella tarda in murine macrophage is dependent on the type III secretion systemEdwardsiella tarda is a pathogen with a broad host range that infects both animals and humans. Resistance to phagocytic killing may be involved in the pathogenicity of this bacterium. We showed that intracellular replication of E. tarda in murine macrophages is dependent on the type III secretion system and induces an anti-apoptotic effect by up-regulating anti-apoptotic NF-kappaB target genes. The wild-type strain replicates within the phagosomal membrane of macrophages ; whereas the type III mutant does not.(2) Microarray analysisMicroarray analysis shows the mRNA expression level of NF-kappaB target genes (e.g. pro-inflammatory cytokines and anti-apoptotic genes) in macrophages infected with the wild-type strain were up-regulated compared to macrophages infected with the type III mutant. Up-regulation of anti-apoptotic NF-kappaB target genes is responsible for the an … More ti-apoptotic activity of E. tarda and is required for intracellular replication in murine macrophages(3) The type III secretion system-dependent repression of NF-kappaB activation to the intracellular growth of Edwardsiella tarda in human epithelial cellsWe next showed that the TTSS is also needed for intracellular growth of the bacterium in human epithelial cells (Hep-2). However, different from the previous microarray analyses on murine macrophages, upregulation of the mRNA expression level of NF-kappaB target genes was not detected in the infected Hep-2 cells. The wild-type E tarda, but not its TTSS mutant, actually repressed the tumor necrosis factor alpha-dependent NF-kappaB activation in an NF-kappaB reporter gene assay. These results suggest TTSS-dependent repression of the NF-kappaB activation in Hep-2 cells infected with E. tarda.Taken together, these results suggest that drug or vaccine specifically targeting the type III secretion system of this bacterium may contribute to decreasing the industrial loss caused by E. tarda infection to cultured fish such as red sea bream and Japanese flounder. Less