Hope R, Potz N A C, Warner M, Fagan E J, Arnold E, Livermore D M
Centre for Infections, Health Protection Agency, 61 Colindale Avenue, London NW9 5EQ, UK.
J Antimicrob Chemother. 2007 Jan;59(1):110-3. doi: 10.1093/jac/dkl431. Epub 2006 Nov 6.
Enterobacteriaceae with extended-spectrum beta-lactamases (ESBLs) are now widespread and simple phenotypic tests are required to detect them in diagnostic laboratories. We investigated the performance of screening methods at 16 hospitals in South-East England.
Sixteen laboratories in South-East England submitted 1195 consecutive Enterobacteriaceae isolates found to be resistant, by their routine methods, to any or all of cefpodoxime, ceftazidime and cefotaxime. These isolates were re-tested centrally with various cephalosporin/clavulanate combinations and with multiplex PCR for bla(CTX-M) and bla(AmpC) alleles.
Screening methods among the laboratories were the following: cefpodoxime discs alone (1 site); cefpodoxime, cefotaxime and ceftazidime discs (9 sites) or agar dilution (1 site); Phoenix (2 sites), Vitek 1 (1 site) and Vitek 2 (2 sites). A total of 8% of isolates submitted based on disc tests proved fully cephalosporin-susceptible, compared with 3% sent based on tests with automated systems and none of those sent based on agar dilution tests. Among isolates submitted solely on cefpodoxime resistance 256/372 (69%) proved cephalosporin-susceptible or had only borderline resistance with no clear mechanism demonstrable; this proportion decreased to 28/160 (18%) for those submitted on the basis of resistance to ceftazidime, 18/122 (15%) for those resistant to cefotaxime and 26/496 (5%) for those resistant to both cefotaxime and ceftazidime. The inference of ESBL production by Vitek 2 had the best agreement with reference laboratory results.
Many isolates found resistant only to cefpodoxime at the source sites proved not to have ESBLs or AmpC; screening with cefotaxime and ceftazidime allowed better specificity for identification of mechanism-based resistance, as did the automated systems. Cefpodoxime disc tests nevertheless remain a useful primary screen for laboratories prepared only to test one agent.
产超广谱β-内酰胺酶（ESBLs）的肠杆菌科细菌现已广泛存在，诊断实验室需要简单的表型检测方法来检测它们。我们调查了英格兰东南部16家医院筛查方法的性能。
英格兰东南部的16家实验室提交了1195株连续分离的肠杆菌科细菌，这些细菌通过其常规方法被发现对头孢泊肟、头孢他啶和头孢噻肟中的任何一种或全部耐药。这些分离株在中心实验室用各种头孢菌素/克拉维酸组合以及针对bla(CTX-M)和bla(AmpC)等位基因的多重PCR进行重新检测。
各实验室的筛查方法如下：单独使用头孢泊肟纸片（1家实验室）；头孢泊肟、头孢噻肟和头孢他啶纸片（9家实验室）或琼脂稀释法（1家实验室）；Phoenix系统（2家实验室）、Vitek 1系统（1家实验室）和Vitek 2系统（2家实验室）。基于纸片试验提交的分离株中，共有8%被证明对头孢菌素完全敏感，而基于自动化系统检测提交的分离株中这一比例为3%，基于琼脂稀释试验提交的分离株中则无一例敏感。仅基于头孢泊肟耐药提交的分离株中，256/372（69%）被证明对头孢菌素敏感或仅为临界耐药，且无明确可证实的耐药机制；基于头孢他啶耐药提交的分离株中这一比例降至28/160（18%），基于头孢噻肟耐药提交的分离株中为18/122（15%），基于头孢噻肟和头孢他啶均耐药提交的分离株中为26/496（5%）。Vitek 2系统对ESBL产生的推断与参考实验室结果的一致性最好。
在来源实验室仅发现对头孢泊肟耐药的许多分离株被证明不产ESBLs或AmpC；用头孢噻肟和头孢他啶进行筛查以及自动化系统对基于机制的耐药性鉴定具有更好的特异性。然而，对于仅准备检测一种药物的实验室，头孢泊肟纸片试验仍然是一种有用的初步筛查方法。
