Identification of natural mutations responsible for altered infection phenotypes of Salmonella enterica clinical isolates using cell line infection screens. Salmonella enterica subsp. enterica

Salmonella enterica is one of the major causes of foodborne diseases globally, affecting millions of people and resulting in thousands of fatal cases per year. Initial steps of Salmonella pathogenesis involve adhesion to and invasion of host epithelial cells. In this study we screened 127 clinical Salmonella isolates from serovars Gallinarum, Dublin, Choleraesuis, Typhimurium and Enteritidis, representing various host specificity range using the following three cell lines: human Caco-2, porcine IPEC-J2 and chicken CHIC-8E11. Next, 30 isolates with altered infectivity were used for genomic analyses and 14 genes and novel mutations associated with high or low infectivity were identified. The functions of candidate genes were: virulence gene expression regulation, synthesis of cell wall or membrane elements or cell membrane components. The role of several of these genes in Salmonella adhesion and invasion to cells has not been investigated so far. Genes dksA, sanA, ompD and yidR were selected for further analyses, which confirmed their role in host cell adhesion and invasion. Furthermore, to get an overview of which processes contribute to altered infection phenotypes, transcriptomic analysis was carried out. Transcriptomes were sequenced for S. Enteritidis and S. Typhimurium, with two highly infective and two marginally infective isolates of each serovar. Expression profiles for the isolates with altered infection phenotypes revealed the importance of T3SS expression levels in the determination of isolate infection phenotype. Taken together, these data indicate a new role in cell host infection for genes or gene variants previously not associated with adhesion and invasion to the epithelial cells.