Incursion of the DT104 multiresistance locus into Salmonella choleraesuis

Abstract

The increasing prevalence of multi-drug resistance in pathogenic bacteria is a significant problem for food safety. Salmonella enterica serovar Typhimurium DT104, which is a global health concern and infects a broad range of mammalian hosts, has been shown to carry a chromosomal integron (SGI-1) which encodes multiple antibiotic resistance: ampicillin, chloramphenicol, strepto- mycin, sulfonamides, and tetracycline (ACSSuT). The portion of this integron encoding antibiotic resistance is 13 kb and the remaining 30 kb is of unknown function but may contribute to hyper- virulence in DT104. The SGI-1 antibiotic resistance gene cluster has subsequently been identified in other serovars suggesting lateral transfer of this element. Host-adapted Salmonella have been assessed for the SGI-1 integron. Isolates of S. choleraesuis, the swine-adapted serovar, with the ACSSuT phenotype have been recovered from pooled clinical isolates. Full sequencing of the SGI- 1 is underway. Characterization of this integron provides insight into antibiotic resistance, viru- lence, and SGI-1 transfer between pathogens. Introduction Multidrug resistant (MDR) Salmonella are a major concern in veterinary medicine, food safety, and agricultural practices. Salmonella enterica serovar Typhimurium DT104, which is a global health concern and infects a broad range of mammalian hosts, has been shown to carry a chromosomal integron (SGI-1) which encodes multiple antibiotic resistance: ampicillin, chloram- phenicol, streptomycin, sulfonamides, and tetracycline (ACSSuT). This 43 kb integron is composed of a 13 kb region encoding antibiotic resistance adjacent to 30 kb of unknown function. This larger region contains 15 unknown ORFs as well as genes related to mating pair formation and DNA