Giraud Etienne, Blanc Guillaume, Bouju-Albert Agnes, Weill François-Xavier, Donnay-Moreno Claire
Unité Mixte de Recherche INRA-ENVN Chimiothérapie Aquacole et Environnement, Ecole Nationale Vétérinaire, Atlanpôle, La Chantrerie, BP40706, 44307 Nantes, Cedex 03, France 2Unité de Biodiversité des Bactéries Pathogènes Emergentes, INSERM U 389, Institut Pasteur, 75724 Paris Cedex 15, France.
J Med Microbiol. 2004 Sep;53(Pt 9):895-901. doi: 10.1099/jmm.0.45579-0.
The mechanisms of resistance to quinolone and epidemiological relationships among A. salmonicida strains isolated from diseased fish in French marine farms from 1998 to 2000 were investigated. The quinolone resistance-determining regions of the gyrA and parC genes of 12 clinical A. salmonicida isolates with different levels of quinolone susceptibility were sequenced. MICs were determined in the presence of the efflux pump inhibitor (EPI) Phe-Arg beta-naphthylamide and E(max) values (MIC without EPI/MIC in the presence of EPI) were calculated. Isolates fell into two classes: (i) those that had a wild-type gyrA gene with oxolinic acid MIC </= 0.5, flumequine MIC </= 1 and ciprofloxacin MIC </= 0.25 micro g ml(-1); and (ii) those that had a single mutation in gyrA encoding Asp-87 --> Asn with oxolinic acid MIC >/= 2, flumequine MIC >/= 4 and ciprofloxacin MIC >/= 0.125 micro g ml(-1). No mutations were found in parC. High E(max) values obtained for flumequine and oxolinic acid (up to 16 and 8, respectively, for the most resistant isolates of the two classes) indicated an important contribution of efflux to the resistance phenotype. Flumequine accumulation experiments confirmed that high E(max) values were associated with a much lower level of accumulation. PCR/RFLP assays conducted on 34 additional isolates showed the presence of a mutation at codon 87 of gyrA in nearly all the quinolone-resistant isolates. This finding, together with PFGE typing results, strongly suggests a common clonal origin of these quinolone-resistant isolates.
对1998年至2000年从法国海洋养殖场患病鱼类中分离出的杀鲑气单胞菌菌株的喹诺酮耐药机制及流行病学关系进行了研究。对12株具有不同喹诺酮敏感性水平的临床杀鲑气单胞菌分离株的gyrA和parC基因的喹诺酮耐药决定区进行了测序。在存在外排泵抑制剂（EPI）苯丙氨酸 - 精氨酸β - 萘酰胺的情况下测定最低抑菌浓度（MIC），并计算E(max)值（无EPI时的MIC/存在EPI时的MIC）。分离株分为两类：（i）具有野生型gyrA基因的菌株，恶喹酸MIC≤0.5、氟甲喹MIC≤1且环丙沙星MIC≤0.25μg ml(-1)；（ii）gyrA编码天冬氨酸87→天冬酰胺的单突变菌株，恶喹酸MIC≥2、氟甲喹MIC≥4且环丙沙星MIC≥0.125μg ml(-1)。在parC中未发现突变。氟甲喹和恶喹酸获得的高E(max)值（两类中最耐药的分离株分别高达16和8）表明外排在耐药表型中起重要作用。氟甲喹积累实验证实高E(max)值与低得多的积累水平相关。对另外34株分离株进行的PCR/RFLP分析表明，几乎所有喹诺酮耐药分离株的gyrA第87位密码子存在突变。这一发现与脉冲场凝胶电泳（PFGE）分型结果一起，强烈提示这些喹诺酮耐药分离株有共同的克隆起源。
