SRA

Salmonella Enteritidis is the second most common serovar associated with iNTS disease in sub-Saharan Africa. Previously, genomic and phylogenetic characterisation of S. Enteritidis isolates from human bloodstream led to the discovery of the Western African and Central/Eastern African (CEAC) clades, which were distinct from the gastroenteritis-associated Global Epidemic clade (GEC). The African S. Enteritidis clades have unique genetic signatures that include genomic degradation, novel prophage repertoires and multi-drug resistance, but the molecular basis for the enhanced propensity of African S. Enteritidis to cause bloodstream infection is poorly understood. We used transposon insertion sequencing to identify the genetic determinants of the GEC representative strain P125109 and the CEAC representative strain D7795 for growth in three in vitro conditions (LB or minimal NonSPI2 and InSPI2 growth media), and for survival and replication in RAW 264.7 murine macrophages. We identified 207 in vitro-required genes that were common to both S. Enteritidis strains and also required by S. Typhimurium, S. Typhi and Escherichia coli, and 63 genes that were only required by individual S. Enteritidis strains. Similar types of genes were required by both P125109 and D7795 for optimal growth in particular media. Screening the transposon libraries during macrophage infection identified 177 P125109 and 201 D7795 genes that contribute to bacterial survival and replication in mammalian cells. The majority of these genes have proven roles in Salmonella virulence. Our analysis also revealed candidate strain-specific macrophage fitness genes, some of which represent potential novel Salmonella virulence factors.