Reticulate Evolution Among the Group I Salmonellae: An Ongoing Role for Horizontal Gene Transfer

Abstract

Salmonella enterica is responsible for 1.4 million cases of foodborne salmonellosis in the United States annually making it the number one causative agent of bacterial foodborne illnesses (CDC, 2007). Infection can occur after eating undercooked meat, poultry and eggs that have been contaminated with Salmonella (CDC, 2007). In recent years several outbreaks have occurred in the United States that were associated with Salmonella contamination of produce, the most recent being a S. enterica Saintpaul outbreak associated with tomatoes, jalapeno and serrano peppers that sickened over 1400 individuals (CDC, 2008). The movement of several serovars of Salmonella into previously naive niches (i.e., producegrowing environs) suggests that the pathogen is readily adapting to new environments. An understanding of the reticulate evolutionary mechanisms that underpin the acquisition and composition of the requisite genetic and phenotypic features of Salmonella is essential to more accurate risk assessment of this pathogen (Hohmann, 2001).