Infection of Mice by Salmonella enterica Serovar Enteritidis Involves Additional Genes That Are Absent in the Genome of Serovar Typhimurium

Abstract

ABSTRACTSalmonella entericaserovar Enteritidis causes a systemic, typhoid-like infection in newly hatched poultry and mice. In the present study, a library of 54,000 transposon mutants ofS.Enteritidis phage type 4 (PT4) strain P125109 was screened for mutants deficient in thein vivocolonization of the BALB/c mouse model using a microarray-based negative-selection screening. Mutants in genes known to contribute to systemic infection (e.g.,Salmonellapathogenicity island 2 [SPI-2],aro,rfa,rfb,phoP, andphoQ) and enteric infection (e.g., SPI-1 and SPI-5) in this and otherSalmonellaserovars displayed colonization defects in our assay. In addition, a strong attenuation was observed for mutants in genes and genomic islands that are not present inS.Typhimurium or in most otherSalmonellaserovars. These genes include a type I restriction/modification system (SEN4290toSEN4292), thepegfimbrial operon (SEN2144AtoSEN2145B), a putative pathogenicity island (SEN1970 to SEN1999), and a type VI secretion system remnantSEN1001, encoding a hypothetical protein containing a lysin motif (LysM) domain associated with peptidoglycan binding. Proliferation defects for mutants in these individual genes and in exemplar genes for each of these clusters were confirmed in competitive infections with wild-typeS.Enteritidis. A ΔSEN1001mutant was defective for survival within RAW264.7 murine macrophagesin vitro. Complementation assays directly linked theSEN1001gene to phenotypes observedin vivoandin vitro. The genes identified here may perform novel virulence functions not characterized in previousSalmonellamodels.