Detection of AmpC Beta-Lactamase in Escherichia coli: Comparison of Three Phenotypic Confirmation Assays and Genetic Analysis
Detection of AmpC Beta-Lactamase in Escherichia coli: Comparison of Three Phenotypic Confirmation Assays and Genetic Analysis
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DOI：
10.1128/jcm.00091-11
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发表时间：
2011-08-01
影响因子：
9.4
通讯作者：
Bloemberg, G. V.
中科院分区：
文献类型：
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作者：
Peter-Getzlaff, S.;Polsfuss, S.;Bloemberg, G. V.
在大肠杆菌中产生AmpC酶活性的机制有两种，即AmpC酶基因启动子和衰减区的突变导致AmpC酶的过度表达和携带质粒的AmpC酶基因的获得。在这项研究中，我们分析了51株对阿莫西林-克拉维酸、哌拉西林-他唑巴坦或产AmpC酶的超广谱头孢菌素敏感性降低的临床分离株。比较3种表型AmpC酶确认试验(头孢西丁-氯唑西林纸片扩散法、头孢西丁-EDTA纸片扩散法和AmpC Etest法)对AmpC酶活性的检测。对所有51株菌株进行了染色体AmpC基因启动子/衰减区的突变分析和携带质粒的AmpC基因的聚合酶链式反应检测。共有21/51(41%)的大肠埃希菌被认为是真正的AmpC酶产生菌。12/21株菌株的AmpC酶活性是由于染色体AmpC酶基因启动子/衰减子突变引起的，8/21株菌株携带有质粒携带的AmpC酶基因。其中一株既含有ampC启动子突变，又含有携带AmpC基因的质粒。所有三种表型试验都能够正确检测出大多数(90%)AmpC酶阳性菌株。头孢西丁耐药性是一个可区分的参数，可检测出20/21株产AmpC酶菌株。21株AmpC酶阳性菌株中有9株对超广谱头孢菌素类药物敏感，如头孢曲松、头孢他啶和头孢噻肟。考虑到2010年CLSI指南中的隆起区直径断裂点，2/21株AmpC酶阳性菌株被归类为对超广谱头孢菌素敏感。
Two mechanisms account for AmpC activity in Escherichia coli, namely, mutations in the ampC promoter and attenuator regions resulting in ampC overexpression and acquisition of plasmid-carried ampC genes. In this study, we analyzed 51 clinical E. coli isolates with reduced susceptibility to amoxicillin-clavulanic acid, piperacillin-tazobactam, or extended-spectrum cephalosporins for the presence of AmpC production. Three phenotypic AmpC confirmation assays (cefoxitin-cloxacillin disk diffusion test, cefoxitin-EDTA disk diffusion test, and AmpC Etest) were compared for the detection of AmpC activity. All 51 isolates were characterized genetically by mutational analysis of the chromosomal ampC promoter/attenuator region and by PCR detection of plasmid-carried ampC genes. Altogether, 21/51 (41%) E. coli isolates were considered true AmpC producers. AmpC activity due to chromosomal ampC promoter/attenuator mutations was found in 12/21 strains, and plasmid-carried ampC genes were detected in 8/21 isolates. One strain contained both ampC promoter mutations and a plasmid-carried ampC gene. All three phenotypic tests were able to detect the majority (> 90%) of AmpC-positive strains correctly. Cefoxitin resistance was found to be a discriminative parameter, detecting 20/21 AmpC-producing strains. Susceptibility to extended-spectrum cephalosporins, e. g., ceftriaxone, ceftazidime, and cefotaxime, was found in 9 of the 21 AmpC-positive strains. Considering the elevated zone diameter breakpoints of the 2010 CLSI guidelines, 2/21 AmpC-positive strains were categorized as susceptible to extended-spectrum cephalosporins.