Different pathways to acquiring resistance genes illustrated by the recent evolution of IncW plasmids.

Departamento de Biología Molecular e Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria-CSIC-IDICAN, C. Herrera Oria s/n, 39011 Santander, Spain.
Antimicrobial Agents and Chemotherapy (Impact Factor: 4.57). 05/2008; 52(4):1472-80. DOI: 10.1128/AAC.00982-07
Source: PubMed

ABSTRACT DNA sequence analysis of five IncW plasmids (R388, pSa, R7K, pIE321, and pIE522) demonstrated that they share a considerable portion of their genomes and allowed us to define the IncW backbone. Among these plasmids, the backbone is stable and seems to have diverged recently, since the overall identity among its members is higher than 95%. The only gene in which significant variation was observed was trwA; the changes in the coding sequence correlated with parallel changes in the corresponding TrwA binding sites at oriT, suggesting a functional connection between both sets of changes. The present IncW plasmid diversity is shaped by the acquisition of antibiotic resistance genes as a consequence of the pressure exerted by antibiotic usage. Sequence comparisons pinpointed the insertion events that differentiated the five plasmids analyzed. Of greatest interest is that a single acquisition of a class I integron platform, into which different gene cassettes were later incorporated, gave rise to plasmids R388, pIE522, and pSa, while plasmids R7K and pIE321 do not contain the integron platform and arose in the antibiotic world because of the insertion of several antibiotic resistance transposons.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Horizontal gene transfer (HGT) is a major force driving bacterial evolution. Because of their ability to cross inter-species barriers, bacterial plasmids are essential agents for HGT. This ability, however, poses specific requisites on plasmid physiology, in particular the need to overcome a multilevel selection process with opposing demands. We analyzed the transcriptional network of plasmid R388, one of the most promiscuous plasmids in Proteobacteria. Transcriptional analysis by fluorescence expression profiling and quantitative PCR revealed a regulatory network controlled by six transcriptional repressors. The regulatory network relied on strong promoters, which were tightly repressed in negative feedback loops. Computational simulations and theoretical analysis indicated that this architecture would show a transcriptional burst after plasmid conjugation, linking the magnitude of the feedback gain with the intensity of the transcriptional burst. Experimental analysis showed that transcriptional overshooting occurred when the plasmid invaded a new population of susceptible cells. We propose that transcriptional overshooting allows genome rebooting after horizontal gene transfer, and might have an adaptive role in overcoming the opposing demands of multilevel selection.
    PLoS Genetics 02/2014; 10(2):e1004171. · 8.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The IncHI1 plasmid pSRC27-H from Salmonella enterica serovar Typhimurium carries a region containing several genes that confer resistance to different antibiotics, and this resistance region is in the same position as related resistance regions in a group of sequenced IncHI1 plasmids from various sources that includes pHCM1. Four further additional segments are found in pHCM1 relative to another IncHI1 plasmid, R27. Using PCR or DNA sequencing to detect the presence or absence of each of these additional segments in the same position in the IncHI1 backbone, plasmid pSRC27-H was found to include them. However, in one case the additional segment was smaller in pSRC27-H, lacking a transposon carrying a second resistance region in pHCM1. The sequences of IncHI1 plasmids, pO111_1 and pMAK1, were also examined and found to share the same or closely related additional segments. The structure of the additional material in pHCM1, pO111_1 and pMAK1 was examined, and potential novel transposons were identified. These additional segments define an IncHI1 lineage (pHCM1, pO111_1, pMAK1, pSRC27-H) which we designated type 2 to distinguish it from type 1 (R27, pAKU_1, pP-stx-12). A segment from the Escherichia coli genome and an adjacent copy of IS1 in pHCM1 was defined by comparison to pO111_1 and pMAK1, which lack it. pSRC27-H also lacks it. This structure is present in the same position in R27 and type 1 plasmids, but in the opposite orientation, and appears to have been incorporated via IS1-mediated transposition. The PCRs developed provide a simple means of distinguishing type 1 and type 2 IncHI1 plasmids based on the presence or absence of variable regions.
    Plasmid 04/2013; · 1.28 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: AimsTransmissible plasmids captured from stream and soil bacteria conferring resistance to tetracycline in Pseudomonas were evaluated for linked resistance to antibiotics used in the treatment of human infections.Methods and ResultsCells released from stream sediments and soils were conjugated with a rifampicin resistant, plasmid-free P. putida recipient and selected on tetracycline and rifampicin. Each transconjugant contained a single 50-80 kb plasmid. Resistance to 11 antibiotics, in addition to tetracycline, was determined for the stream transconjugants using a modification of the Stokes disk diffusion antibiotic susceptibility assay. Nearly half of plasmids conferred resistance to six or more antibiotics. Resistance to streptomycin, gentamicin, and/or ticarcillin was conferred by a majority of the plasmids, and resistance to additional human clinical use antibiotics such as piperacillin/tazobactam, ciprofloxacin, and aztreonam was observed. MICs of 16 antibiotics for representative sediment and soil transconjugants revealed large increases, relative to the P. putida recipient, for 11 of 16 antibiotics tested, including the expanded spectrum antibiotics cefotaxime and ceftazidime, as well as piperacillin/tazobactam, lomefloxacin, and levofloxacin.Conclusions Resistance to multiple antibiotics – including those typically used in clinical Pseudomonas and enterobacterial infections – can be conferred by transmissible plasmids in streams and soils.Significance and Impact of StudySelective pressure exerted by the use of one antibiotic, such as the common agricultural antibiotic tetracycline, may result in the persistence of linked genes conferring resistance to important human clinical antibiotics. This may impact the spread of resistance to human use antibiotics even in the absence of direct selection.This article is protected by copyright. All rights reserved.
    Journal of Applied Microbiology 05/2014; · 2.20 Impact Factor

Full-text (2 Sources)

Available from
Jun 4, 2014

Similar Publications