Apfalter Petra, Assadian Ojan, Daxböck Florian, Hirschl Alexander M, Rotter Manfred L, Makristathis Athanasios
Department of Clinical Microbiology, Institute of Hygiene and Medical Microbiology, Medical University Vienna, Vienna, Austria.
J Antimicrob Chemother. 2007 May;59(5):854-9. doi: 10.1093/jac/dkm060. Epub 2007 Mar 8.
The aims of this study were to determine the prevalence of extended-spectrum beta-lactamases (ESBLs) in AmpC-carrying Enterobacter spp. in a tertiary care university hospital in Vienna, Austria, and to implement a cost-effective strategy to detect ESBLs in this particular genus on a routine basis.
Clinical Enterobacter isolates (n=208) were investigated by means of (i) an inhibitor-potentiated diffusion test using cefpodoxime, (ii) an expanded double disc diffusion synergy test (discs of cefotaxime, ceftazidime, cefpodoxime and cefepime placed around amoxicillin/clavulanic acid), (iii) the Etest ESBL screening method and (iv) the cefoxitin-cefotaxime antagonist test. Cefepime MICs were determined by separate Etests.
Of 208 isolates, 76 (37%), 18 (9%) and 92 (44%) were derepressed, partially derepressed and inducible AmpC producers, respectively. Eight (4%) ESBL-producing Enterobacter strains could be detected, all of which would have been detected using disc-based tests. Six out of eight strains were genetically not related, as assessed by random amplification of polymorphic DNA. Typing results were confirmed by means of enterobacterial repetitive intergenic consensus PCR. The MIC(90) of cefepime was not different in ESBL carriers (range 2-4 mg/L), and was especially low in inducible AmpC producers (0.125 mg/L). More than half of all Enterobacter isolates (n=110; 53%) were partly derepressed or fully inducible AmpC producers. In the absence of cefoxitin, they appeared susceptible or intermediately susceptible to cefazolin (n=8; 9%), cefuroxime (n=75; 81.5%), ceftazidime (n=91; 99%), cefotaxime (n=92; 100%), cefpodoxime (n=75; 81.5%) and cefepime (n=91; 99%).
Susceptibility to third-generation cephalosporins would have been falsely assumed in more than half of all Enterobacter isolates, but ESBL in Enterobacter is currently rare in our institution. Integration of multiple double disc tests into the routine antibiogram seems a reliable approach to screen for emerging resistance mechanisms. Etests did not provide additional information in this study.
本研究旨在确定奥地利维也纳一家三级护理大学医院中携带AmpC酶的肠杆菌属细菌中广谱β-内酰胺酶（ESBLs）的流行情况，并实施一种具有成本效益的策略，以便在日常工作中常规检测该特定菌属中的ESBLs。
对临床分离的肠杆菌菌株（n = 208）进行了如下检测：（i）使用头孢泊肟的抑制剂增强扩散试验；（ii）扩展双纸片扩散协同试验（将头孢噻肟、头孢他啶、头孢泊肟和头孢吡肟纸片置于阿莫西林/克拉维酸纸片周围）；（iii）Etest ESBL筛选方法；（iv）头孢西丁-头孢噻肟拮抗试验。通过单独的Etest测定头孢吡肟的最低抑菌浓度（MIC）。
在208株分离菌株中，分别有76株（37%）、18株（9%）和92株（44%）为去阻遏型、部分去阻遏型和诱导型AmpC酶产生菌。可检测到8株（4%）产ESBL的肠杆菌菌株，所有这些菌株均可通过基于纸片的试验检测到。通过随机扩增多态性DNA评估，8株菌株中有6株在基因上不相关。通过肠杆菌重复基因间共识PCR证实了分型结果。头孢吡肟的MIC90在ESBL携带者中无差异（范围为2 - 4 mg/L），在诱导型AmpC酶产生菌中尤其低（0.125 mg/L）。所有肠杆菌分离株中超过一半（n = 110；53%）为部分去阻遏型或完全诱导型AmpC酶产生菌。在没有头孢西丁的情况下，它们对头孢唑林（n = 8；9%）、头孢呋辛（n = 75；81.5%）、头孢他啶（n = 91；99%）、头孢噻肟（n = 92；100%）、头孢泊肟（n = 75；81.5%）和头孢吡肟（n = 91；99%）表现出敏感或中介敏感。
超过一半的肠杆菌分离株可能会被错误地认为对第三代头孢菌素敏感，但目前在我们机构中肠杆菌中产ESBL的情况很少见。将多种双纸片试验整合到常规抗菌谱检测中似乎是一种可靠的方法，用于筛查新出现的耐药机制。在本研究中，Etest未提供额外信息。
