Antimicrobial Agents Research Group, Department of Immunity and Infection, The Medical School, The University of Birmingham, Birmingham, B15 2TT, United Kingdom.
J Bacteriol. 2010 Mar;192(6):1607-16. doi: 10.1128/JB.01517-09. Epub 2010 Jan 15.
The transcriptomes of Salmonella enterica serovar Typhimurium SL1344 lacking a functional ramA or ramR or with plasmid-mediated high-level overexpression of ramA were compared to those of the wild-type parental strain. Inactivation of ramA led to increased expression of 14 SPI-1 genes and decreased expression of three SPI-2 genes, and it altered expression of ribosomal biosynthetic genes and several amino acid biosynthetic pathways. Furthermore, disruption of ramA led to decreased survival within RAW 264.7 mouse macrophages and attenuation within the BALB/c ByJ mouse model. Highly overexpressed ramA led to increased expression of genes encoding multidrug resistance (MDR) efflux pumps, including acrAB, acrEF, and tolC. Decreased expression of 34 Salmonella pathogenicity island (SPI) 1 and 2 genes, decreased SipC production, decreased adhesion to and survival within macrophages, and decreased colonization of Caenorhabditis elegans were also seen. Disruption of ramR led to the increased expression of ramA, acrAB, and tolC, but not to the same level as when ramA was overexpressed on a plasmid. Inactivation of ramR had a more limited effect on pathogenicity gene expression. In silico analysis of a suggested RamA-binding consensus sequence identified target genes, including ramR, acrA, tolC, sipABC, and ssrA. This study demonstrates that the regulation of a mechanism of MDR and expression of virulence genes show considerable overlap, and we postulate that such a mechanism is dependent on transcriptional activator concentration and promoter sensitivity. However, we have no evidence to support the hypothesis that increased MDR via RamA regulation of AcrAB-TolC gives rise to a hypervirulent strain.
鼠伤寒沙门氏菌 SL1344 中功能丧失的 ramA 或 ramR 或通过质粒介导的高水平过表达 ramA 的转录组与野生型亲本菌株的转录组进行了比较。ramA 的失活导致 14 个 SPI-1 基因的表达增加和 3 个 SPI-2 基因的表达减少，并改变了核糖体生物合成基因和几个氨基酸生物合成途径的表达。此外，ramA 的缺失导致 RAW 264.7 小鼠巨噬细胞内的存活率降低，并在 BALB/c ByJ 小鼠模型中减弱。高过表达 ramA 导致编码多药耐药（MDR）外排泵的基因表达增加，包括 acrAB、acrEF 和 tolC。还观察到 34 个沙门氏菌致病性岛（SPI）1 和 2 基因的表达减少，SipC 产生减少，对巨噬细胞的黏附和存活减少，以及秀丽隐杆线虫的定植减少。ramR 的缺失导致 ramA、acrAB 和 tolC 的表达增加，但不如质粒上过表达 ramA 时的水平高。ramR 的失活对致病性基因表达的影响更为有限。对建议的 RamA 结合保守序列的计算机分析确定了靶基因，包括 ramR、acrA、tolC、sipABC 和 sssA。本研究表明，MDR 机制的调节和毒力基因的表达存在相当大的重叠，我们假设这种机制依赖于转录激活剂浓度和启动子敏感性。然而，我们没有证据支持增加 MDR 通过 RamA 调节 AcrAB-TolC 导致超级毒力菌株的假说。
