Effects of a novel pathogenicity-related gene product of Salmonella, SEp22, on the viability of Salmonella in its environments

SEp 22表达的潜在调节机制在从家禽养殖场分离的沙门氏菌肠道致病菌株中进一步研究。SEp 22的表达依赖于营养丰富的培养基如Luria-Bertani培养基（LB）中的生长阶段，并且在对数期很少，但在对数后期至稳定期迅速增加。北方印迹或RT-PCR分析显示，在这些生长阶段，SEp 22 mRNA的表达先于SEp 22蛋白的合成而增加，但稍晚于RNA聚合酶σ因子σ32表达的增加。而σ70的表达与SEp 22无关。通过将沙门氏菌转移到新鲜的LB中来循环重复SEp 22中的这些变化。相反，当在营养贫乏的培养基如M-9培养基中培养时，即使在稳定期也没有观察到SEp 22的诱导，这通过向M-9培养基中添加LB而部分恢复。我们一直在研究LB中支持在这些条件下诱导SEp 22的营养因子，并且已经从这些因子中排除了葡萄糖或一些氨基酸。综上所述，这些结果表明，SEp 22的表达是转录调控的，沙门氏菌的环境分离株，即使它可能导致宿主动物的致病性，并不总是成为致病性的营养不良的环境中，由于缺乏SEp 22的表达。

Mechanisms underlying regulation of SEp22 expression were further studied in pathogenic strains of Salmonella Enteritidis, isolated from poultry farms. Expression of SEp22 was dependent on the growth phases in nutritionally enriched culture medium like Luria-Bertani medium(LB), and was scarce in logarithmic phase but became rapidly increased in late-logarithmic to stationary phases. Northern blot or RT-PCR analysis of SEp22 mRNA revealed that it increased prior to the synthesis of SEp22 protein but slightly later than the increase of RNA polymerase σ factor, σ32, expression in these growth phases. However, expression of σ70 was not related with SEp22. These changes in SEp22 were cyclically repeated by transferring Salmonella into fresh LB. In contrast, induction of SEp22 was not observed even in stationary phases when cultured in nutritionally poor medium like M-9 medium, which was in part restored by addition of LB to M-9 medium. We have been examining the nutrition factor(s) in LB which supports induction of SEp22 under these conditions, and have excluded glucose or some amino acids from such factor(s). Taken together, these results suggest that expression of SEp22 is transcriptionally regulated and that environmental isolate of Salmonella, even if it potentially causes pathogenicity to host animals, does not always become pathogenic in nutritionally poor environment due to lack of expression of SEp22.