Bedenić Branka, Ladavac Ranko, Vranić-Ladavac Mirna, Barišić Nada, Karčić Natalie, Sreter Katherina Bernadette, Mihaljević Slobodan, Bielen Luka, Car Haris, Beader Nataša
1Department of Microbiology, School of Medicine, University of Zagreb, Zagreb, Croatia; 2Department of Clinical and Molecular Microbiology, Zagreb University Hospital Centre, Zagreb, Croatia; 3Department of Nephrology, Pula General Hospital, Pula, Croatia; 4Department of Microbiology, Public Health Institute of Istria County, Pula, Croatia; 5Department of Clinical Immunology, Pulmonology and Rheumatology, Sestre milosrdnice University Hospital Centre, Zagreb, Croatia; 6Department of Anesthesiology, Zagreb University Hospital Centre, Zagreb, Croatia; 7Department of Internal Medicine, Zagreb University Hospital Centre, Zagreb, Croatia; 8Zagreb Secondary Medical School, Zagreb, Croatia.
Acta Clin Croat. 2019 Mar;58(1):113-118. doi: 10.20471/acc.2019.58.01.15.
Phenotypic detection of metallo-β-lactamases (MBLs) in is a serious challenge to clinical microbiologists. MBLs are inhibited by metal chelators such as ethylenediaminetetraacetic acid) (EDTA). Production of MBLs cannot be recognized based on resistance phenotype. Therefore, phenotypic tests using EDTA are recommended. The aim of this study was to investigate the sensitivity and specificity of inhibitor based tests (EDTA) for detection of MBL. A total of 172 strains (123 carbapenemase positive and 49 carbapenemase negative) were analyzed. Phenotypic detection of MBLs was performed by the combined disk test with EDTA (CDT-EDTA) and EPI-dilution test (EPI-DT). Both tests were positive in all 11 isolates possessing VIM-1 MBL, showing 100% sensitivity. However, false positive results were observed in strains with class D carbapenemases using both tests, i.e. all OXA-23 and OXA-24/40 producing organisms and most OXA-58 positive strains (77% with CDT-EDTA . 65% with EPI-DT). False positive results can occur because oxacillinases are converted to a less active state in the presence of EDTA, leading to augmentation of the inhibition zone around the carbapenem disk or reduction of carbapenem minimum inhibitory concentrations. This study showed high sensitivity but low specificity of phenotypic methods in the detection of MBLs.
金属β-内酰胺酶（MBLs）的表型检测对临床微生物学家来说是一项严峻挑战。MBLs可被金属螯合剂如乙二胺四乙酸（EDTA）抑制。基于耐药表型无法识别MBLs的产生。因此，推荐使用基于EDTA的表型试验。本研究的目的是调查基于抑制剂的试验（EDTA）检测MBL的敏感性和特异性。共分析了172株菌株（123株碳青霉烯酶阳性和49株碳青霉烯酶阴性）。通过EDTA联合纸片试验（CDT-EDTA）和EPI-稀释试验（EPI-DT）进行MBLs的表型检测。在所有11株携带VIM-1 MBL的分离株中，两种试验均为阳性，显示出100%的敏感性。然而，在使用两种试验检测携带D类碳青霉烯酶的菌株时均观察到假阳性结果，即所有产OXA-23和OXA-24/40的菌株以及大多数OXA-58阳性菌株（CDT-EDTA检测为77%，EPI-DT检测为65%）。出现假阳性结果的原因可能是在EDTA存在下，氧青霉烯酶转变为活性较低的状态，导致碳青霉烯纸片周围抑菌圈增大或碳青霉烯最低抑菌浓度降低。本研究表明表型方法检测MBLs时敏感性高但特异性低。
