Characterisation of multidrug-resistant Salmonella Typhimurium 4,[5],12:i:- DT193 strains carrying a novel genomic island adjacent to the thrW tRNA locus

Abstract

In 2006, monophasic, multidrug-resistant Salmonella enterica spp. enterica serovar 4,[5],12:i:- strains appeared as a novel serotype in Germany, associated with large diffuse outbreaks and increased need for hospitalisation. The emerging 4,[5],12:i:- strains isolated from patients in Germany belong mainly to phage type DT193 according to the Anderson phage typing scheme for S. Typhimurium (STM) and exhibit at least a tetra-drug resistance. The strains have been shown to harbour STM-specific Gifsy-1, Gifsy-2, and ST64B prophages. Furthermore, the extensive sequence similarity of the tRNA regions between one characterised 4,[5],12:i:- phage type DT193 and the S. Typhimurium LT2 strain as well as the STM-specific position of an IS 200 element within the fliA- fliB intergenic region ( Echeita et al., 2001) prompted us to classify them as a monophasic variant of S. Typhimurium. In 2008, the monophasic variant represented 42.2% of all S. Typhimurium isolates from human analysed at the National Reference Centre. Searching for insertions in tRNA sites resulted in the detection of an 18.4-kb fragment adjacent to the thrW tRNA locus, exhibiting a lower G+C content compared to the LT2 genome. Sequence analysis identified 17 potential ORFs. Some of them showed high similarity to enterobacterial phage sequences and sequences from Shigella boydii, Sh. dysenteriae, avian pathogenic Escherichia coli and other Escherichia spp. The biological function of this novel island with respect to virulence properties and metabolic functions is under investigation.