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JAC Advance Access published online on August 13, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn323
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© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
The online version of this article has been published under an open access model. Users are entitled to use, reproduce, disseminate, or display the open access version of this article for non-commercial purposes provided that: the original authorship is properly and fully attributed; the Journal and Oxford University Press are attributed as the original place of publication with the correct citation details given; if an article is subsequently reproduced or disseminated not in its entirety but only in part or as a derivative work this must be clearly indicated. For commercial re-use, please contact journals.permissions@oxfordjournals.org

Original research

Transfer of antimicrobial resistance plasmids from Klebsiella pneumoniae to Escherichia coli in the mouse intestine

Susanne Schjørring, Carsten Struve and Karen A. Krogfelt*

Department of Bacteriology, Mycology and Parasitology, Statens Serum Institut, Artillerivej 5, 2300 Copenhagen S, Denmark

Received 25 April 2008; returned 3 July 2008; revised 11 June 2008; accepted 11 July 2008

* Corresponding author. Tel: +45-3268-3745; Fax: +45-3268-3147; E-mail: kak{at}ssi.dk

Objectives and methods: Klebsiella pneumoniae is a nosocomial pathogen and is considered the most common Gram-negative bacterium that exhibits multiple antimicrobial resistances. In this study, the transfer of antimicrobial resistance genes from the clinical multiresistant K. pneumoniae MGH75875 isolate was assessed in vitro and in vivo in an intestinal colonization animal model. The ability to colonize and transfer was tested under different antimicrobial treatments. The frequency of the horizontal gene transfer was also examined in vitro.

Results: The clinical isolate of K. pneumoniae colonized the intestine of mice at levels up to 109 cfu/g faeces in antimicrobial-treated mice. In mice without antimicrobial treatment, the strain quickly decreased to below the detection limit due to competitive exclusion by the indigenous mouse flora. Onset of antimicrobial treatment gave immediate rise to detectable levels of the strain in the faeces of up to 109 cfu/g faeces. The experiment clearly shows that the treatment selects resistant strains and gives advantages to colonize the gastrointestinal tract. Furthermore, high transfer frequency of different plasmids was observed during colonization of the mouse intestine. The blaSHV and blaTEM genotypes were transferred to both an indigenous recipient in the in vivo setting and to an MG1655 Escherichia coli recipient strain in vitro.

Conclusions: K. pneumoniae is an excellent colonizer of the intestine and is extremely promiscuous with respect to the transferability of its numerous plasmids. Antimicrobial treatment enhances the selection of resistant strains and results in an increase in the resistance gene pool, which ultimately raises the risk of spreading resistance genes.

Key Words: MGH78578 , horizontal gene transfer , streptomycin-treated mice , gastrointestinal tract , indigenous flora , selective pressure


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