ClinicalSalmonellaTyphimurium ST34 with metal tolerance genes and an IncHI2 plasmid carryingoqxAB-aac(6′)-Ib-crfrom Europe

Sir, Fluoroquinolones are critical antibiotics for treating severe Salmonella infections, and the widespread of resistant isolates included in diverse epidemiological scenarios and carrying plasmid-mediated quinolone resistance (PMQR) is a global threat.1,2 Among PMQR mechanisms, those encoded by oqxAB and aac(6′)-Ib-cr genes are of special concern as they also confer reduced susceptibility to other antibiotics (oqxAB: chloramphenicol, trimethoprim, olaquindox; aac(6′)-Ib-cr: aminoglycosides) and biocides [oqxAB: quaternary ammonium compounds (QACs)].2,3 Although oqxAB ± aac(6′)-Ib-cr are prevalent and widespread in Asia, where olaquindox is still widely used in animal production, they remain scarce in Europe.1,2,4–6 Here we describe the molecular characterization of clinical ciprofloxacin-resistant Salmonella enterica Typhimurium with concomitant presence of oqxAB and aac(6′)-Ib-cr recovered for the first time in Europe. Two ciprofloxacin-resistant (MIC 2 mg/L) S. enterica Typhimurium isolates carrying oqxAB and aac(6′)-Ib-cr genes were isolated from faeces of two young children (1 and 2 years old) admitted to a Portuguese hospital in September 2012. Further characterization included the study of susceptibility to 11 other antimicrobial agents and β-lactamase and carbapenemase production by disc diffusion, Etest and/or microdilution methods (EUCAST/CLSI guidelines) and the Blue-Carba test. Screening of genes encoding resistance to antibiotics (including quinolone resistance-determining region mutations and PMQR) or tolerance to biocides/metals found in the animal setting (e.g. feed/disinfectants) was performed by PCR and/or sequencing.7–9 Determination of transferability of PMQR genes (conjugation at 25/30/37°C and transformation) and characterization of integrons and plasmid backbones were performed by PCR, plasmid-based replicon typing, plasmid MLST (pMLST; http://pubmlst.org/plasmid/), hybridization (I-CeuI/S1-PFGE nuclease) and/or sequencing.1,7,8 The oqxAB-aac(6′)-Ib-cr genetic environment was characterized by PCR mapping based on known sequences.1 Clonal analysis was assessed by XbaI-PFGE8 and MLST (http://mlst.warwick.ac.uk/mlst/dbs/Senterica).