Abstract
BackgroundThe Salmonella genomic island 1 (SGI1) is a Salmonella enterica-derived integrative mobilizable element (IME) containing various complex multiple resistance integrons identified in several S. enterica serovars and in Proteus mirabilis. Previous studies have shown that SGI1 transfers horizontally by in trans mobilization in the presence of the IncA/C conjugative helper plasmid pR55.Methodology/Principal FindingsHere, we report the ability of different prevalent multidrug resistance (MDR) plasmids including extended-spectrum β-lactamase (ESBL) gene-carrying plasmids to mobilize the multidrug resistance genomic island SGI1. Through conjugation experiments, none of the 24 conjugative plasmids tested of the IncFI, FII, HI2, I1, L/M, N, P incompatibility groups were able to mobilize SGI1 at a detectable level (transfer frequency <10−9). In our collection, ESBL gene-carrying plasmids were mainly from the IncHI2 and I1 groups and thus were unable to mobilize SGI1. However, the horizontal transfer of SGI1 was shown to be specifically mediated by conjugative helper plasmids of the broad-host-range IncA/C incompatibility group. Several conjugative IncA/C MDR plasmids as well as the sequenced IncA/C reference plasmid pRA1 of 143,963 bp were shown to mobilize in trans SGI1 from a S. enterica donor to the Escherichia coli recipient strain. Depending on the IncA/C plasmid used, the conjugative transfer of SGI1 occurred at frequencies ranging from 10−3 to 10−6 transconjugants per donor. Of particular concern, some large IncA/C MDR plasmids carrying the extended-spectrum cephalosporinase bla CMY-2 gene were shown to mobilize in trans SGI1.Conclusions/SignificanceThe ability of the IncA/C MDR plasmid family to mobilize SGI1 could contribute to its spread by horizontal transfer among enteric pathogens. Moreover, the increasing prevalence of IncA/C plasmids in MDR S. enterica isolates worldwide has potential implications for the epidemic success of the antibiotic resistance genomic island SGI1 and its close derivatives.
Highlights
Acquisition of foreign DNA by horizontal gene transfer (HGT) is a crucial mechanism that allows bacteria to acquire new traits, and it represents a key driving force in bacterial evolution
The identification of Salmonella genomic island 1 (SGI1) in the chromosome of several S. enterica serovars, i.e. Agona, Cerro, Derby, Dusseldorf, Emek, Haifa, Infantis, Kedougou, Kentucky, Kiambu, Kingston, Meleagridis, Newport, Paratyphi B, Tallahassee, Typhimurium, Virchow, and in P. mirabilis suggested that SGI1 might be horizontally mobilized by conjugative elements concomitantly borne by field strains [11,12,13,14,15]
Mobilization experiments were undertaken to determine whether SGI1 was mobilizable in trans by different conjugative plasmids previously described as spreading among multidrug resistance (MDR) Salmonella strains and/or other pathogenic Enterobacteriaceae [16]
Summary
Acquisition of foreign DNA by horizontal gene transfer (HGT) is a crucial mechanism that allows bacteria to acquire new traits, and it represents a key driving force in bacterial evolution. After excision of SGI1 from the Salmonella chromosome, the conjugative mobilization in trans by the conjugative helper IncA/C plasmid pR55 occurs between donor and recipient strains. Mobilization experiments were undertaken to determine whether SGI1 was mobilizable in trans by different conjugative plasmids previously described as spreading among MDR Salmonella strains and/or other pathogenic Enterobacteriaceae [16].
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