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JAC Advance Access published online on November 26, 2009
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkp424
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© The Author 2009. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Original research

Smaqnr, a new chromosome-encoded quinolone resistance determinant in Serratia marcescens

C. Velasco1,*, J. M. Rodríguez-Martínez1, A. Briales2, P. Díaz de Alba1, J. Calvo3 and A. Pascual1,2

1 Department of Microbiology, University of Seville, Seville, Spain 2 Service of Microbiology, University Hospital Virgen Macarena, Seville, Spain 3 Service of Microbiology, University Hospital Marqués de Valdecilla, Santander, Spain

Received 14 August 2009; returned 25 September 2009; revised 29 October 2009; accepted 2 November 2009

* Corresponding author. Tel: +34-954-55-28-63; Fax: +34-954-37-74-13; E-mail: cvelasco{at}us.es

Objectives: A new pentapeptide repeat (PRP) protein, named SmaQnr, from the clinically relevant species Serratia marcescens, which decreased susceptibility to quinolones when expressed in Escherichia coli, is reported herein.

Methods: In silico analysis revealed the presence of a gene encoding a Qnr-like protein that shares 80% amino acid identity with QnrB1 in the S. marcescens strain Db11. Fragments carrying the coding region and the upstream non-coding sequences of eight clinical isolates were cloned and expressed in E. coli. MIC values of quinolones were determined. RT–PCR was used to study expression of these genes in their natural host. Southern hybridization was used to explore the presence of the gene in the genus Serratia.

Results: Recombinant plasmids encoding SmaQnr reduced susceptibility to fluoroquinolones and nalidixic acid in both E. coli ATCC 25922 and DH10B. Sequences upstream of these genes contain a LexA box. Conventional RT–PCR showed transcription of the analysed Smaqnr genes in their natural hosts. Southern blot analysis suggests the presence of similar genes in several species of the genus Serratia.

Conclusions: SmaQnr conferred a reduced susceptibility phenotype against fluoroquinolones in E. coli. These data provide evidence of its possible role in quinolone resistance in S. marcescens. This Gram-negative species may constitute a reservoir for qnr-like quinolone resistance genes.

Key Words: pentapeptide repeat protein , Qnr , fluoroquinolones


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