Transposon Mutagenesis of Salmonella enterica Serovar Enteritidis Identifies Genes That Contribute to Invasiveness in Human and Chicken Cells and Survival in Egg Albumen

Abstract

ABSTRACTSalmonella entericaserovar Enteritidis is an important food-borne pathogen, and chickens are a primary reservoir of human infection. While most knowledge aboutSalmonellapathogenesis is based on research conducted onSalmonella entericaserovar Typhimurium,S. Enteritidis is known to have pathobiology specific to chickens that impacts epidemiology in humans. Therefore, more information is needed aboutS. Enteritidis pathobiology in comparison to that ofS. Typhimurium. We used transposon mutagenesis to identifyS. Enteritidis virulence genes by assay of invasiveness in human intestinal epithelial (Caco-2) cells and chicken liver (LMH) cells and survival within chicken (HD-11) macrophages as a surrogate marker for virulence. A total of 4,330 transposon insertion mutants of an invasive G1 Nalrstrain were screened using Caco-2 cells. This led to the identification of attenuating mutations in a total of 33 different loci, many of which include genes previously known to contribute to enteric infection (e.g.,Salmonellapathogenicity island 1 [SPI-1], SPI-4, SPI-5, CS54,fliH,fljB,csgB,spvR, andrfbMN) inS. Enteritidis and otherSalmonellaserovars. Several genes or genomic islands that have not been reported previously (e.g., SPI-14,ksgA,SEN0034,SEN2278, andSEN3503) or that are absent inS. Typhimurium or in most otherSalmonellaserovars (e.g.,pegD,SEN1152,SEN1393, andSEN1966) were also identified. Most mutants with reduced Caco-2 cell invasiveness also showed significantly reduced invasiveness in chicken liver cells and impaired survival in chicken macrophages and in egg albumen. Consequently, these genes may play an important role during infection of the chicken host and also contribute to successful egg contamination byS. Enteritidis.