美国宠物分离得到的广谱头孢菌素耐药大肠埃希菌中染色体和质粒介导的氟喹诺酮耐药机制。
Chromosomal and plasmid-mediated fluoroquinolone resistance mechanisms among broad-spectrum-cephalosporin-resistant Escherichia coli isolates recovered from companion animals in the USA.
机构信息
Division of Microbiology, National Center for Toxicological Research, US Food and Drug Administration, Jefferson, AR, USA.
出版信息
J Antimicrob Chemother. 2013 May;68(5):1019-24. doi: 10.1093/jac/dks514. Epub 2013 Jan 9.
OBJECTIVES
To determine the prevalence of plasmid-mediated quinolone resistance (PMQR) determinants and investigate mutations in gyrase and topoisomerase genes that may contribute to increased fluoroquinolone resistance in canine and feline Escherichia coli isolates in the USA that displayed reduced susceptibility to extended-spectrum cephalosporins. This study was undertaken because previous epidemiological studies identified a potential correlation between extended-spectrum cephalosporins and fluoroquinolone resistance.
METHODS
Isolates (n = 54) with reduced susceptibility to ceftazidime or cefotaxime were screened by PCR for the presence of PMQR determinants and gyrase and topoisomerase genes were sequenced. Isolates were further characterized by conjugation and phylogenetic analyses.
RESULTS
PMQR determinants aac(6')-Ib-cr, qnrS and qepA were identified in 30, 23 and 5 isolates, respectively. Multiple mutations were identified in the quinolone resistance-determining region, including the novel substitutions of Glu-84 → Ala and Leu-88 → Gln in ParC and Arg-432 → Ser and Glu-460 → Val in ParE. The isolate that exhibited the highest level of enrofloxacin resistance (MIC > 256 mg/L) had a double mutation in gyrA (Ser-83 → Leu and Asp-87 → Asn) and a triple mutation in parC (Ser-80 → Ile, Glu-84 → Gly and a novel mutation, Leu-88 → Gln). The presence of PMQR genes increased the ciprofloxacin MIC values 4-fold to 8-fold in transconjugants relative to the recipient strain. Approximately 39% of the isolates belonged to phylogenetic group D and 30% to group B2, which typically contain an increased number of virulence determinants compared with other groups.
CONCLUSIONS
Novel mutations in topoisomerase genes and PMQR determinants aac(6')-Ib-cr, qnrS and qepA genes were detected among extended-spectrum β-lactamase-producing E. coli in the USA.
目的
确定质粒介导的喹诺酮耐药（PMQR）决定因素的流行率，并研究拓扑异构酶基因突变，这些突变可能导致美国犬猫大肠杆菌分离株对氟喹诺酮的耐药性增加，这些分离株对扩展谱头孢菌素的敏感性降低。进行这项研究是因为之前的流行病学研究表明，扩展谱头孢菌素和氟喹诺酮耐药之间存在潜在的相关性。
方法
通过 PCR 筛选对头孢他啶或头孢噻肟敏感性降低的分离株，以检测 PMQR 决定因素和拓扑异构酶基因的存在，并对这些基因进行测序。通过接合和系统发育分析进一步对分离株进行特征分析。
结果
在 30、23 和 5 株分离株中分别鉴定出 PMQR 决定因素 aac(6')-Ib-cr、qnrS 和 qepA。喹诺酮耐药决定区存在多种突变，包括 ParC 中新型取代 Glu-84→Ala 和 Leu-88→Gln 以及 ParE 中 Arg-432→Ser 和 Glu-460→Val。表现出最高恩诺沙星耐药水平（MIC＞256 mg/L）的分离株在 gyrA 中存在双重突变（Ser-83→Leu 和 Asp-87→Asn）和 parC 中三重突变（Ser-80→Ile、Glu-84→Gly 和新型突变 Leu-88→Gln）。与受体株相比，转导子中 PMQR 基因的存在使环丙沙星 MIC 值增加了 4 至 8 倍。大约 39%的分离株属于 D 群，30%属于 B2 群，与其他群相比，B2 群通常含有更多的毒力决定因素。
结论
在美国产超广谱β-内酰胺酶大肠杆菌中发现了拓扑异构酶基因突变和 PMQR 决定因素 aac(6')-Ib-cr、qnrS 和 qepA 基因的新型突变。
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