title: Molecular characterization of antimicrobial susceptibility of Salmonella isolates: First identification of a plasmid carrying qnrD or oqxAB in Taiwan.
abstract: OBJECTIVE
  The aim of this study is to characterize antibiotic-nonsusceptible Salmonella isolates in Taiwan.
  
  
  METHODS
  A total of 76 Salmonella isolates showing lower susceptibility to cephalosporins or quinolones were identified from 1416 clinical isolates from 1999 to 2008. Minimal inhibitory concentrations for selected antimicrobial agents were tested by the agar dilution method. Antibiotic resistance-related genes were determined by polymerase chain reaction (PCR) combined with sequencing. Southern blotting, conjugation tests, and transformation tests were used to characterize plasmid-mediated quinolone resistance (PMQR) determinants.
  
  
  RESULTS
  The observed nonsusceptible phenotypes of 76 isolates were against cefoxitin (57.9%), cefotaxime (43.4%), ceftazidime (40.8%), ceftriaxone (42.1%), cefepime (5.3%), ciprofloxacin (80.3%), and levofloxacin (81.6%). Among 44 cephalosporin-resistant isolates, TEM-1, CMY-2, CMY-14, CTX-M-3-like and CTX-M-15-like determinants were present in 31 (70.5%), 32 (72.7%), 1 (2.3%), 1 (2.3%), and 1 (2.3%) of isolates, respectively. PCR screening for PMQR genes of 62 quinolone-nonsusceptible isolates revealed the presence of qnrS, qnrD, aac(6')-Ib-cr, and oqxAB in 3 (4.8%), 2 (3.2%), 1 (1.6%), and 10 (16.1%) isolates, respectively. Among 36 isolates showing high resistance to quinolones, S83F/D87N and S83F/D87G amino acid substitutions of GyrA were found in 29 (80.6%) and 6 (16.7%) isolates, respectively. Moreover, among quinolone highly resistant isolates, eight (22.2%) of isolates showed over-expression of the PAβN-sensitive efflux pump. Transformants and transconjugants harboring qnrD- or oqxAB-plasmids showed decreased susceptibility to quinolones.
  
  
  CONCLUSIONS
  GyrA mutations are the major mechanisms associated with quinolone-resistant Salmonella isolates in Taiwan. Overproduction of efflux pump genes and the presence of qnr and oqxAB play additional roles in reduced susceptibility to quinolones.
authors.affiliation: Department of Medical Laboratory Science and Biotechnology, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Cheng-Yen
authors.initials: CY
authors.lastname: Kao
authors.affiliation: Department of Medical Laboratory Science and Biotechnology, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Chun-An
authors.initials: CA
authors.lastname: Chen
authors.affiliation: Department of Medical Laboratory Science and Biotechnology, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Yi-Fang
authors.initials: YF
authors.lastname: Liu
authors.affiliation: Department of Medical Laboratory Science and Biotechnology, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Hsiu-Mei
authors.initials: HM
authors.lastname: Wu
authors.affiliation: Centers for Disease Control, Taichung, Taiwan.
authors.forename: Chien-Shun
authors.initials: CS
authors.lastname: Chiou
authors.affiliation: Department of Pathology, National Cheng Kung University Hospital, Tainan, Taiwan.
authors.forename: Jing-Jou
authors.initials: JJ
authors.lastname: Yan
authors.affiliation: Department of Medical Laboratory Science and Biotechnology, College of Medicine, National Cheng Kung University, Tainan, Taiwan; Center of Infectious Disease and Signaling Research, National Cheng Kung University, Tainan, Taiwan. Electronic address: jjwu@mail.ncku.edu.tw.
authors.forename: Jiunn-Jong
authors.initials: JJ
authors.lastname: Wu
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002511:Cephalosporins / Q000494:pharmacology*; D027081:DNA Gyrase / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D005838:Genotype; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction; D015363:Quinolones / Q000494:pharmacology*; D012475:Salmonella / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D013624:Taiwan; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D001426:Bacterial Proteins; D002511:Cephalosporins; D015363:Quinolones; D001618:beta-Lactamases; D027081:DNA Gyrase
keywords: Salmonella; cephalosporin; oqxAB; plasmid-mediated quinolone resistance; qnrD