Abstract
Outbreaks of salmonellosis linked to the consumption of vegetables have been disproportionately associated with strains of serovar Newport. We tested the hypothesis that strains of sv. Newport have evolved unique adaptations to persistence in plants that are not shared by strains of other Salmonella serovars. We used a genome-wide mutant screen to compare growth in tomato fruit of a sv. Newport strain from an outbreak traced to tomatoes, and a sv. Typhimurium strain from animals. Most genes in the sv. Newport strain that were selected during persistence in tomatoes were shared with, and similarly selected in, the sv. Typhimurium strain. Many of their functions are linked to central metabolism, including amino acid biosynthetic pathways, iron acquisition, and maintenance of cell structure. One exception was a greater need for the core genes involved in purine metabolism in sv. Typhimurium than in sv. Newport. We discovered a gene, papA, that was unique to sv. Newport and contributed to the strain’s fitness in tomatoes. The papA gene was present in about 25% of sv. Newport Group III genomes and generally absent from other Salmonella genomes. Homologs of papA were detected in the genomes of Pantoea, Dickeya, and Pectobacterium, members of the Enterobacteriacea family that can colonize both plants and animals.
Highlights
Salmonellosis outbreaks linked to the consumption of fruits, leafy green vegetables and sprouts became an important public health issue over the last decade, defying the traditional notion that this pathogen is only associated with products of animal origin (Teplitski et al, 2009; Hernandez-Reyes and Schikora, 2013; Jackson et al, 2013; Wiedemann et al, 2014; Bennett et al, 2015)
Frontiers in Microbiology | www.frontiersin.org de Moraes et al Salmonella Functional Genomics in Tomatoes associated with vine-stalk vegetables
Newport strain in tomatoes to previous results obtained for a Typhimurium strain
Summary
Salmonellosis outbreaks linked to the consumption of fruits (tomatoes, cucumbers, cantaloupes), leafy green vegetables and sprouts became an important public health issue over the last decade, defying the traditional notion that this pathogen is only associated with products of animal origin (Teplitski et al, 2009; Hernandez-Reyes and Schikora, 2013; Jackson et al, 2013; Wiedemann et al, 2014; Bennett et al, 2015). Newport as the predominant serovar involved in outbreaks traced to vegetables. It was responsible for 57% of outbreaks associated with all fresh vegetables, and for 29% of outbreaks. Tomatoes were a major source of salmonellosis outbreaks, and were implicated in up to 90% of outbreaks linked to vine-stalk vegetables, with sv. An analysis of outbreak occurrence from 1990 to 2010 identified 15 outbreaks that were associated with fresh tomatoes, and sv.
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