RNA Sequencing Reveals Differences between the Global Transcriptomes of Salmonella enterica Serovar Enteritidis Strains with High and Low Pathogenicities

Salmonella enterica serovar Enteritidis is one of the important causes of bacterial food-borne gastroenteritis worldwide. Field strains of S. Enteritidis are relatively genetically homogeneous; however, they show extensive phenotypic diversity and differences in virulence potential. RNA sequencing (RNA-Seq) was used to characterize differences in the global transcriptome between several genetically similar but phenotypically diverse poultry-associated field strains of S. Enteritidis grown in laboratory medium at avian body temperature (42 degrees C). These S. Enteritidis strains were previously characterized as high-pathogenicity (HP; n = 3) and low-pathogenicity (LP; n = 3) strains based on both in vitro and in vivo virulence assays. Using the negative binomial distribution-based statistical tools edgeR and DESeq, 252 genes were identified as differentially expressed in LP strains compared with their expression in the HP strains (P< 0.05). A majority of genes (235, or 93.2%) showed significantly reduced expression, whereas a few genes (17, or 6.8%) showed increased expression in all LP strains compared with HP strains. LP strains showed a unique transcriptional profile that is characterized by significantly reduced expression of several transcriptional regulators and reduced expression of genes involved in virulence (e. g., Salmonella pathogenicity island 1 [SPI-1], SPI-5, and fimbrial and motility genes) and protection against osmotic, oxidative, and other stresses, such as iron-limiting conditions commonly encountered within the host. Several functionally uncharacterized genes also showed reduced expression. This study provides a first concise view of the global transcriptional differences between field strains of S. Enteritidis with various levels of pathogenicity, providing the basis for future functional characterization of several genes with potential roles in virulence or stress regulation of S. Enteritidis.