Abstract
Salmonella enterica serovar 4,[5],12:i:- is a monophasic variant of S. Typhimurium incapable of expressing the second-phase flagellar antigen (fljAB operon), and it is recognized to be one of the most prevalent serovars causing human infections. A clonal lineage characterized by phage type DT193, PulseNet PFGE profile STYMXB.0131 and multidrug resistance to ampicillin, streptomycin, sulphonamides and tetracycline (R-type ASSuT) is commonly circulating in Europe. In this study we determined the deletions affecting the fljAB operon and the resistance region responsible for the R-type ASSuT in a strain of Salmonella enterica serovar 4,5,12:i:- DT193/STYMXB.0131, through an approach based on PCRs and Southern blot hybridization of genomic DNA. Using a set of nine specific PCRs, the prevalence of the resistance region was assessed in a collection of 144 S. enterica serovar 4,[5],12:i:-/ASSuT/STYMXB.0131 strains isolated from Germany, Switzerland and Italy. A 28 kb-region is embedded between the loci STM2759 and iroB, replacing the DNA located in between, including the fljAB operon. It encompasses the genes blaTEM−1, strA-strB, sul2 and tet(B) responsible for the R-type ASSuT together with genes involved in plasmid replication and orfs of unknown function characteristically located on IncH1 plasmids. Its location and internal structure is fairly conserved in S. enterica serovar 4,[5],12:i:-/ASSuT/STYMXB.0131 strains regardless of the isolation source or country. Hence, in the S. enterica serovar 4,[5],12:i:-/ASSuT/STYMXB.0131 clonal lineage widespread in Germany, Switzerland and Italy, a resistance region derived from IncH1 plasmids has replaced the chromosomal region encoding the second flagellar phase and is an example of the stabilization of new plasmid-derived genetic material due to integration into the bacterial chromosome.
Highlights
Multidrug resistant Salmonella enterica subsp. enterica serovar 4,[5],12:i:, a monophasic variant of S
A clonal lineage of S. 4,[5],12:i:- characterized by phage type DT193, PulseNet pulsed field gel electrophoresis (PFGE) profile STYMXB.0131 (XBAI.0027 according to ECDC PFGE nomenclature; van Walle, 2013) and resistance to ampicillin, streptomycin, sulphonamides, and tetracycline (R-type ASSuT) is circulating in Europe (Hauser et al, 2010; Hopkins et al, 2010; Lucarelli et al, 2010; Gallati et al, 2013; Argüello et al, 2014; Barco et al, 2014)
Instead in the Italian S. 4,5,12:i:- strain with PulseNet PFGE-XbaI profile STYMXB.0079 (XBAI.0096 according to ECDC) (Lucarelli et al, 2012) R-type ASSuT, the fljAB operon is affected by IS26 insertion and the genes responsible for resistance are located in two genomic regions, named resistance region (RR) 1 and RR2 inserted into two adjacent loci of the bacterial chromosome
Summary
Multidrug resistant Salmonella enterica subsp. enterica serovar 4,[5],12:i:- (subsequently referred as S. 4,[5],12:i:-), a monophasic variant of S. 4,[5],12:i:- characterized by phage type DT193, PulseNet pulsed field gel electrophoresis (PFGE) profile STYMXB.0131 (XBAI.0027 according to ECDC PFGE nomenclature; van Walle, 2013) and resistance to ampicillin, streptomycin, sulphonamides, and tetracycline (R-type ASSuT) is circulating in Europe (Hauser et al, 2010; Hopkins et al, 2010; Lucarelli et al, 2010; Gallati et al, 2013; Argüello et al, 2014; Barco et al, 2014) In this clonal lineage neither the resistance region nor the deletion affecting the fljAB operon has been determined. S. 4,[5],12:i:-/ASSuT/STYMXB.0131 strains (mainly phage type DT193) does not harbor equivalent RR1 and RR2 regions
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