JAC Advance Access first published online on September 23, 2009
This version published online on September 25, 2009
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkp347
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Original research |
Decreased fluoroquinolone susceptibility in mutants of Salmonella serovars other than Typhimurium: detection of novel mutations involved in modulated expression of ramA and soxS
1 Institute for Food Quality and Food Safety, University of Veterinary Medicine Hannover, Bischofsholer Damm 15, 30173 Hannover, Germany 2 Institute of Farm Animal Genetics, Friedrich-Loeffler-Institute (FLI), Höltystr. 10, 31535 Neustadt-Mariensee, Germany 3 INRA, UR1282, Infectiologie Animale et Sante Publique, IASP, Nouzilly F-37380, France
Received 5 August 2009; accepted 28 August 2009
* Corresponding author. Institute for Food Quality and Food Safety, University of Veterinary Medicine Hannover, Bischofsholer Damm 15, 30173 Hannover, Germany. Tel: +49-511-856-7513; Fax: +49-511-856-7513; E-mail: corinna.kehrenberg{at}tiho-hannover.de
Objectives: Mutants of five Salmonella enterica serovars were investigated for structural changes in regulatory regions known to be involved in the up-regulation of efflux pumps.
Methods: Five Salmonella field isolates and mutants, in which efflux pump inhibitor tests previously pointed towards an up-regulation of efflux, plus one negative control were included in the study. MIC values were determined of antibiotics that were indicative of AcrAB overexpression. The regulatory regions acrRA, soxRS, marORAB, acrSE and ramRA of original strains and mutants were sequenced and compared. The gene expression of acrA, tolC, ramA and soxS was assessed by quantitative real-time PCR. Conjugation experiments and tet gene PCRs were performed to explain unexpected variations in MIC values of tetracycline.
Results: In four mutant strains, changes in the ramRA regulatory region, causing up-regulation of ramA, were detected. These changes comprised point mutations and deletions of 10 or 15 bp within the ramR gene and a single bp exchange located in the binding site of the RamR protein in Salmonella Infantis, Paratyphi and Livingstone mutants. An insertion of 49 bp within the soxR gene was involved in soxS up-regulation and enhanced efflux activity in the fifth mutant from Salmonella Virchow. The loss of tetracycline resistance in one Salmonella Paratyphi mutant could be explained by the loss of a plasmid carrying a tet(A) gene.
Conclusions: Changes in the ramR-ramA region as well as in the soxR gene occur in mutants of Salmonella serovars other than Typhimurium and seem to be involved in the up-regulation of efflux activity.
Key Words: Salmonella enterica , efflux pumps , resistance
The original version was incorrect. On page 2, line 13 of the right-hand column: ‘Qiagen’ should have read ‘Qiagen, Hilden, Germany’.