Pendle S, Jelfs P, Olma T, Su Y, Gilroy N, Gilbert G L
Centre for Infectious Diseases and Microbiology, Institute of Clinical Pathology and Medical Research, Westmead Hospital, Westmead, Westmead, New South Wales, Australia.
Clin Microbiol Infect. 2008 Sep;14(9):853-7. doi: 10.1111/j.1469-0691.2008.02052.x.
Between June and November 2004, a vancomycin-resistant Enterococcus faecium (VRE) strain was isolated from 13 patients in the haematology/bone marrow transplant unit. There were difficulties in identifying the organism, which had low-level, inducible vancomycin resistance, and standard screening methods did not reveal carriage in patients or their contacts. These technical failures led to spread of VRE and delays in providing appropriate management, which might otherwise have been avoided. Therefore, we reviewed our laboratory methods and compared three identification systems to determine which would best identify this VRE strain. The VITEK 2 (BioMerieux) correctly identified, as E. faecium, only two of 16 isolates, whereas API Rapid ID 32 Strep (BioMerieux) and Phoenix 100 (Becton Dickinson and Co.) correctly identified 13 of 15 and 12 of 13 isolates tested, respectively. Isolates from urine, tested by the CLSI disk diffusion method, were apparently susceptible or of intermediate susceptibility to vancomycin, upon primary testing. VITEK 2 and Phoenix 100 identified all isolates as vancomycin-resistant, although the MICs, measured by Etest, were in the susceptible range for three of 16 isolates. Reducing the vancomycin concentration in screening media substantially increased the sensitivity for detection of VRE. Isolates were characterized as genotype vanB2/3 by PCR and were indistinguishable from each other by pulsed-field gel electrophoresis. VRE with low-level inducible resistance can be missed by routine screening methods. Better identification and screening methods for detection of low-level vancomycin resistance are needed to improve surveillance and prevent transmission of VRE.
2004年6月至11月期间，血液学/骨髓移植科的13名患者中分离出耐万古霉素屎肠球菌（VRE）菌株。该菌株具有低水平、可诱导的万古霉素耐药性，在鉴定过程中遇到困难，标准筛查方法未发现患者及其接触者携带该菌。这些技术失误导致VRE传播，并延误了适当治疗的提供，而这些情况原本是可以避免的。因此，我们回顾了实验室方法，并比较了三种鉴定系统，以确定哪种系统能最好地鉴定这种VRE菌株。VITEK 2（生物梅里埃公司）仅正确鉴定出16株分离菌中的2株为屎肠球菌，而API Rapid ID 32 Strep（生物梅里埃公司）和Phoenix 100（贝克顿·迪金森公司）分别正确鉴定出所检测的15株中的13株和13株中的12株。通过CLSI纸片扩散法检测尿液中的分离菌，初检时对万古霉素明显敏感或中度敏感。VITEK 2和Phoenix 100将所有分离菌鉴定为耐万古霉素，尽管通过Etest测定的最低抑菌浓度（MIC）对16株中的3株处于敏感范围内。降低筛查培养基中万古霉素的浓度可大幅提高VRE检测的灵敏度。通过PCR将分离菌鉴定为vanB2/3基因型，脉冲场凝胶电泳显示它们彼此无法区分。常规筛查方法可能会漏检具有低水平诱导耐药性的VRE。需要更好的鉴定和筛查方法来检测低水平的万古霉素耐药性，以改善监测并防止VRE传播。
