Regulatory mechanisms of expression of SEp22, a noves pathogenicity-related factor of Salmonella Enteritidis, underlying penetration through intestinal membrane

在肠道沙门氏菌（SE）中，sep22基因在对数生长期早期转录量很小，然后随着细菌的生长逐渐增加，在对数生长期后期达到最大值，通常在接种到新鲜LB培养基后6 - 8 h。另一方面，沙门氏菌的典型毒力因子invA（也是III型分泌系统（TTSS）的重要成员）在细菌开始培养后迅速表达，并且通常在孵育后1 - 2h达到最大值，随后逐渐降低直到第二阶段。这些结果表明，sep22和invA在致病性沙门氏菌细胞中显示出相当不同的调节，其在沙门氏菌对宿主细胞的建立感染期间应发挥不同的作用，即，前者，作为一种保护因子，防止宿主杀死效应分子，而后者则是对主人的一种冒犯。目前正在进行一些实验来证明sep22在沙门氏菌感染中的关键作用，以使用SE的sep22基因敲除突变株KO-5建立回复突变体。关于SEp22表达的营养因子，我们在LB培养基、酪蛋白氨基酸、卷心菜提取物、胎牛血清、蛋黄等中对其中的一些分子进行了表征，证明了多种分子作为营养因子是有效的，并且已经使用HPLC对酪蛋白氨基酸中的一些分子进行了纯化。此外，SEp22蛋白在致病性SE感染Caco-2细胞过程中的表达无明显差异，但在SE与巨噬细胞的粘附过程中起负作用，而在SE对巨噬细胞的侵袭过程中起正作用，提示SEp22在沙门氏菌致病过程中具有多重调节作用。

In a pathogenic strain of Salmonella Enteritidis, (SE), sep22 gene was transcribed very little in early logarithmic phase, then became gradually increased in accordance with the bacterial growth, reaching maximal at the late logarithmic phase usually 6-8 h after inoculation of the bacteria in to fresh LB medium. On the other hand, a typical virulent factor of Salmonella, invA, which is also an important member of Type III secretion system (TTSS), became rapidly expressed after starting cultivation of the bacteria, and became maximal usually 1-2 h after incubation, followed by gradual decrease until stational phase. These results suggest that sep22 and invA show quite distinct regulation in a pathogenic Salmonella cell, which should exert different roles during establishing infection of Salmonella to host cells, i.e., the former, working as a protective factor against killing effector molecules from the host., and the latter, working as an offense factor toward the host. Some trials to prove the pivotal role of sep22 in Salmonella infection are in progress to establish revertants using KO-5 strain, a sep22-gene knock out mutant of SE. Regarding nutritional factors involved in SEp22 expression, we characterized some of them in LB medium, casamino acids, cabbage extracts, fetal bovine serum, egg yolk and so on. A variety of molecules were shown to be effective as a nutritional factors, and some molecules in casamino acids have been purified using HPLC. Besides, SEp22 protein expression in SE strains was shown to be playing negative roles in adhesion of pathogenic SE to macrophages but also positive roles in invasion to the macrophages, although that in SE showed no significant differences in the course of SE infection to Caco-2 cells, suggesting multiple regulatory roles of SEp22 in Salmonella pathogenesis.