title: RamA, a member of the AraC/XylS family, influences both virulence and efflux in Salmonella enterica serovar Typhimurium.
abstract: 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.
authors.affiliation: Antimicrobial Agents Research Group, Department of Immunity and Infection, The Medical School, The University of Birmingham, Birmingham, B15 2TT, United Kingdom.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Bailey
authors.forename: Al
authors.initials: A
authors.lastname: Ivens
authors.forename: Rob
authors.initials: R
authors.lastname: Kingsley
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Cottell
authors.forename: John
authors.initials: J
authors.lastname: Wain
authors.forename: Laura J V
authors.initials: LJ
authors.lastname: Piddock
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D017173:Caenorhabditis elegans / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D005260:Female; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D008264:Macrophages / Q000382:microbiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D018272:Porins; D012480:Salmonella Infections / Q000382:microbiology; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D018272:Porins; D015534:Trans-Activators; C531999:RamA protein, Salmonella typhimurium