The Importance of Mobile Genetic Elements in the Evolution of Salmonella: Pathogenesis, Antibiotic Resistance and Host Adaptation

Since the divergence from Escherichia coli, more than 100 million years ago, Salmonella has acquired by lateral gene transfer a repertoire of genes that confers a set of physiological features that define its particular ecological niche (Ochman and Groisman 1994; Ochman et al., 2000). Some of these chromosomally-encoded genes can be considered as part of the “core genome” of Salmonella (i. e. genes present in all the strains), whereas some other chromosomally-encoded genes are part of the “accessory genome” (i. e. genes present in some of the strains) along with mobile genetic elements such as plasmids, bacteriophages, transposons and integrons. In this chapter we review the role that mobile genetic elements have played in Salmonella evolution, particularly in pathogenicity attributes, antibiotic resistance and host adaptation.