title: Molecular characterization of fluoroquinolone resistance in Haemophilus parasuis isolated from pigs in South China.
abstract: OBJECTIVE
  To perform molecular characterization of fluoroquinolone-resistant Haemophilus parasuis isolated from South China.
  
  
  METHODS
  H. parasuis isolates were investigated for quinolone and fluoroquinolone susceptibility and screened for plasmid-mediated quinolone resistance (PMQR) determinants by PCR amplification and DNA sequence analysis. Additionally, quinolone resistance-determining region (QRDR) mutations of DNA gyrase (gyrA and gyrB) and topoisomerase IV (parC and parE) were determined. The genetic relatedness among the strains was analysed by PFGE.
  
  
  RESULTS
  These H. parasuis isolates showed higher MIC values of nalidixic acid, enrofloxacin, ciprofloxacin, levofloxacin, norfloxacin and lomefloxacin. Moreover, qnrA1, qnrB6 and aac(6')-Ib-cr were present in 2.61%, 0.87% and 2.61% of the 115 isolates, respectively. One strain possessed both aac(6')-Ib-cr and qnrA1. Mutation analysis of QRDRs showed that the resistant strains carried at least one mutation in gyrA (at codon 83 or 87), but no mutation was detected in gyrB. PFGE analysis showed great genetic diversity among these resistant H. parasuis strains.
  
  
  CONCLUSIONS
  The data presented here highlight the presence of qnr and aac(6')-Ib-cr genes in H. parasuis strains from South China. Moreover, the gyrA (at codon 83 or 87) mutation is linked to fluoroquinolone resistance in H. parasuis. Transferable PMQR determinants and multiple target gene mutations play important roles in the fluoroquinolone resistance of H. parasuis. These data provide important insights into the mechanism of fluoroquinolone resistance in H. parasuis, thereby highlighting the usefulness of fluoroquinolones for the treatment and control of this infection.
authors.affiliation: Key Laboratory of Animal Disease Control and Prevention of the Ministry of Agriculture, Key Laboratory of Zoonoses Prevention and control of Guang dong, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, People's Republic of China.
authors.forename: Lili
authors.initials: L
authors.lastname: Guo
authors.forename: Jianmin
authors.initials: J
authors.lastname: Zhang
authors.forename: Chenggang
authors.initials: C
authors.lastname: Xu
authors.forename: Yongda
authors.initials: Y
authors.lastname: Zhao
authors.forename: Tao
authors.initials: T
authors.lastname: Ren
authors.forename: Bin
authors.initials: B
authors.lastname: Zhang
authors.forename: Huiying
authors.initials: H
authors.lastname: Fan
authors.forename: Ming
authors.initials: M
authors.lastname: Liao
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015373:Bacterial Typing Techniques; D002681:China; D016000:Cluster Analysis; D027081:DNA Gyrase / Q000235:genetics; D027101:DNA Topoisomerase IV / Q000235:genetics; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024881:Drug Resistance, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D024841:Fluoroquinolones / Q000494:pharmacology*; D005838:Genotype; D006192:Haemophilus Infections / Q000382:microbiology / Q000662:veterinary*; D044137:Haemophilus parasuis / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D058889:Molecular Typing; D010957:Plasmids; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D024841:Fluoroquinolones; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase