The effect of the Salmonella genomic island 1 on in vitro global gene expression in Salmonella enterica serovar Typhimurium LT2.

A Salmonella genomic island 1 (SGI1) isogenic strain pair was constructed using Salmonella enterica serovar Typhimurium LT2 (ST LT2). Real-time quantitative reverse transcriptase PCR revealed detectable mRNA transcripts for all 44 putative ORFs encoded within the SGI1. The highest levels of transcripts observed in SGI1 encoded ORFs were found in genes conferring antibiotic resistance to ampicillin, streptomycin/spectinomycin, and sulphonamides. Abundant mRNA transcripts, relative to gapA, were also noted for one putative regulatory ORF and seven ORFs of unknown function encoded within SGI1, whose products could represent factors contributing to increases in virulence and/or fitness of the organism. DNA microarray analysis revealed the differential expression of known factors that contribute to virulence in many pathogens. Twenty-two chromosomal genes were significantly upregulated in ST LT2 harboring SGI1, which included increased expression of iron and sialic acid utilization genes. Decreased expression was noted for 15 genes in ST LT2 harboring SGI1, including genes involved in chemotaxis and motility. This is the first report examining gene expression within the SGI1, as well as its potential effect on global gene expression, and sets the foundation for future studies involving the effect of SGI1 in other Salmonella spp.