Salmonella enterica is a globally disseminated pathogen that is the cause of over 100 million infections per year. The resulting diseases caused by S. enterica is dependent upon host susceptibility and infecting serovar. For example, Typhoid fever is a human exclusive disease caused by S. enterica serovar Typhi. Due to the human specific nature of Typhoid fever, there has been extensive use of murine models to understand the mechanism of S. Typhi infections. This model makes use of the typhoid like disease mice develop upon infection by S. enterica serovar Typhimurium, which is so severe that even one infectious bacterium injected intravenously will cause mortality in 100% of animals in just one week post infection. Due to this incredibly severe disease model researchers often use resistant mouse strains or attenuated S. Typhimurium strains to understand adaptive immunity and infection dynamics. Despite the use of these models, and various S. Typhimurium strains, for decades in research, many aspects of Salmonella infection and fundamental biology remain poorly understood. Here, we use a Transposon Insertion Sequencing (TIS) technique to interrogate the essential genomes of widely used S. Typhimurium strains. This technique combines highly saturated transposon mutagenesis with next generation DNA sequencing to identify genes that are essential for bacterial survival and those that when disrupted by the transposon, cause fitness defects. Here, we reveal differential essential pathways between strains and provide a direct link between iron starvation, DNA synthesis and bacterial membrane integrity.