The University of Queensland, School of Veterinary Science, Seddon Building, Slip Road, St Lucia, Brisbane, Qld 4072, Australia.
Vet Microbiol. 2010 Jul 14;143(2-4):329-36. doi: 10.1016/j.vetmic.2009.11.031. Epub 2009 Dec 3.
Fluoroquinolone resistance is becoming more common in veterinary medicine. Resistance is due to a combination of chromosomal and plasmid-mediated fluoroquinolone resistance (PMQR) mechanisms. The aim of the present study was to screen 17 multidrug-resistant Enterobacter isolates obtained from opportunistic infections in companion animals for chromosomal and plasmid-mediated fluoroquinolone resistance determinants and to determine if they are co-located with other antimicrobial resistance genes including beta-lactamases. Phenotypic tests (biochemical identification, organic solvent tolerance testing) were combined with genotypic analysis (PCR, pulsed field gel electrophoresis, sequencing, plasmid isolation and southern blot hybridization) to characterize the molecular basis for fluoroquinolone resistance. Antimicrobial susceptibility was determined by broth microdilution for fluoroquinolone antimicrobials (enrofloxacin, ciprofloxacin, moxifloxacin, marbofloxacin and pradofloxacin) and by disk diffusion for other antimicrobials. Sixteen isolates were resistant to at least one of the five fluoroquinolones tested. Fourteen isolates possessed PMQR determinants which were identified as qnrA1 (n=3) or qnrB2 (n=11), often in combination with aac(6')-1b-cr (n=6). The PMQR genes were localized to large, transferable MDR plasmids often associated with an extended-spectrum beta-lactamase and quinolone resistance was co-transferred with bla(SHV-12) for 10 of the 14 qnr-positive strains. Three isolates had wild-type topoisomerases, 11 had a single point mutation in gyrA (Ser83Phe or Tyr), and three had two mutations; one in gyrA (Ser83Ile) and one in parC (Ser80Ile). PMQR genes in clinical veterinary Enterobacter isolates are co-located with beta-lactamases and other resistance genes on large transferable plasmids. PMQR genes contribute to fluoroquinolone resistance when combined with topoisomerase mutations and efflux.
氟喹诺酮类药物耐药性在兽医领域越来越常见。耐药性是由染色体和质粒介导的氟喹诺酮类药物耐药（PMQR）机制共同作用引起的。本研究的目的是筛选从伴侣动物机会性感染中获得的 17 株多药耐药性肠杆菌，以筛选染色体和质粒介导的氟喹诺酮类药物耐药决定因素，并确定它们是否与其他抗生素耐药基因（包括β-内酰胺酶）共存。表型试验（生化鉴定、有机溶剂耐受试验）与基因分析（PCR、脉冲场凝胶电泳、测序、质粒分离和Southern 印迹杂交）相结合，以确定氟喹诺酮类药物耐药的分子基础。通过肉汤微量稀释法测定氟喹诺酮类抗菌药物（恩诺沙星、环丙沙星、莫西沙星、马波沙星和普拉洛芬）的药敏性，通过纸片扩散法测定其他抗菌药物的药敏性。16 株分离株对至少一种五种测试的氟喹诺酮类药物耐药。14 株分离株携带 PMQR 决定簇，鉴定为 qnrA1（n=3）或 qnrB2（n=11），通常与 aac(6')-1b-cr （n=6）联合。PMQR 基因定位于大型可转移 MDR 质粒上，这些质粒通常与超广谱β-内酰胺酶和喹诺酮类药物耐药基因相关，14 株 qnr 阳性菌株中有 10 株可同时转移 bla(SHV-12)。3 株分离株拓扑异构酶为野生型，11 株 gyrA 单点突变（Ser83Phe 或 Tyr），3 株有两个突变；一个在 gyrA（Ser83Ile），一个在 parC（Ser80Ile）。临床兽医肠杆菌分离株中的 PMQR 基因与大型可转移质粒上的β-内酰胺酶和其他耐药基因共存。当 PMQR 基因与拓扑异构酶突变和外排作用相结合时，会导致氟喹诺酮类药物耐药。
