Localization of the origin of transfer (oriT) for Salmonella Genomic Island 4 (SGI-4) from Salmonella enterica serovar I 4, [5],12:i:.

Salmonella enterica serovar I 4, [5],12:i:- (serovar I 4, [5],12:i:-) is one of the most frequent multidrug-resistant (MDR) Salmonella serovars associated with food-animal production globally, and strains often contain Salmonella genomic island-4 (SGI-4), an integrative conjugative element (ICE) encoding metal tolerance for copper, silver, and arsenic. Horizontal gene transfer (HGT) of SGI-4 from serovar I 4, [5],12:i:- to recipient bacteria results in enhanced metal tolerance for the transconjugants; however, the origin of transfer (oriT) for SGI-4 mobilization is unknown. In this study, the oriT within SGI-4 of MDR serovar I 4, [5],12:i:- strain USDA15WA-1 was identified by: a) cloning an internal region of SGI-4 into a non-mobilizable plasmid and demonstrating HGT to a bacterial recipient, and b) deleting the predicted oriT region of SGI-4 from strain USDA15WA-1 and abolishing SGI-4 transfer. Sequence similarity to oriTSGI-4 was identified in other Enterobacteriaceae, and conjugation of SGI-4 occurred from USDA15WA-1 to Salmonella serovars from serogroups C-E as well as Escherichia coli and Citrobacter. Localization of the SGI-4 oriT enhances our understanding of a DNA region involved in HGT of an ICE in a frequent MDR Salmonella serovar, thereby providing a model to investigate HGT of SGI-4 and dissemination of metal tolerance genes in the food-animal production environment.