JAC Advance Access originally published online on September 19, 2007
Journal of Antimicrobial Chemotherapy 2007 60(5):1146-1150; doi:10.1093/jac/dkm352
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Plasmid-mediated quinolone resistance conferred by qnrS1 in Salmonella enterica serovar Virchow isolated from Turkish food of avian origin
1 Middle East Technical University, Ankara, Turkey 2 Federal Institute for Risk Assessment (BfR), Berlin, Germany 3 Ankara University, Ankara, Turkey
Received 18 May 2007; returned 4 July 2007; revised 13 August 2007; accepted 14 August 2007
* Corresponding author. Tel: +49-30-8412-2057; Fax: +49-30-8412-2000; E-mail: beatriz.guerra{at}bfr.bund.de
Objectives: To study the molecular characteristics of the quinolone and associated ampicillin resistance mechanisms present in Salmonella enterica serovar Virchow isolated from Turkish foods.
Methods: Nine epidemiologically unrelated Salmonella Virchow strains isolated from foods (chicken and minced meat) sold in different markets in Ankara were analysed for their susceptibility to 17 antimicrobials. The strains were typed by PFGE and plasmid profiling and investigated by molecular methods (PCR/sequencing) for the presence of several resistance genes, class 1 integrons and mutations in the quinolone resistance-determining regions. Plasmids conferring quinolone resistance were analysed by restriction fragment length polymorphism (RFLP) analysis, DNA hybridization, sequencing, replicon-typing PCR and mating experiments.
Results: All strains showed nalidixic acid resistance (MIC 
128 mg/L) together with a decreased susceptibility to ciprofloxacin (three strains with an MIC of 1 mg/L and six with an MIC of 0.25 mg/L), associated with mutations within the gyrA gene (Asp-87 
Tyr-87). In three strains, qnrS1 genes were detected. Ampicillin resistance encoded by a blaCTX-M3 gene and/or blaTEM-1-like gene was found in four strains. Three of these strains carried an 
45 kb conjugative plasmid, designated pRQ2006, harbouring qnrS1 and a Tn3-like transposon. Partial sequencing and RFLP of pRQ2006 indicated its similarity to the qnrS1 plasmid pAH03786 found in a Japanese Shigella flexneri 2b isolate.
Conclusions: This is the first study describing the presence of qnrS1 genes in bacterial isolates from Turkey. The pRQ2006 plasmid seems to be more related to the S. flexneri 2b qnrS1 plasmid pAH0376 than to the Salmonella qnrS1-carrying plasmids pINF5 and TPqnrS-2.
Keywords: qnr , fluoroquinolones , antimicrobial resistance , PFGE , resistance plasmids
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