Acta clinica Croatica, Vol. 58. No. 1., 2019.
Original scientific paper
https://doi.org/10.20471/acc.2019.58.01.15
False Positive Phenotypic Detection of Metallo-Beta-Lactamases in Acinetobacter Baumannii
Branka Bedenić
; Department of Microbiology, School of Medicine, University of Zagreb, Zagreb, Croatia; Department of Clinical and Molecular Microbiology, Zagreb University Hospital Centre, Zagreb, Croatia
Ranko Ladavac
; Department of Nephrology, Pula General Hospital, Pula, Croatia
Mirna Vranić-Ladavac
; Department of Microbiology, Public Health Institute of Istria County, Pula, Croatia
Nada Barišić
; Department of Microbiology, Public Health Institute of Istria County, Pula, Croatia
Natalie Karčić
; Department of Microbiology, Public Health Institute of Istria County, Pula, Croatia
Katherina Bernadette Sreter
; Department of Clinical Immunology, Pulmonology and Rheumatology, Sestre milosrdnice University Hospital Centre, Zagreb, Croatia
Slobodan Mihaljević
; Department of Anesthesiology, Zagreb University Hospital Centre, Zagreb, Croatia
Luka Bielen
; Department of Internal Medicine, Zagreb University Hospital Centre, Zagreb, Croatia
Haris Car
; Zagreb Secondary Medical School, Zagreb, Croatia
Nataša Beader
; Department of Microbiology, School of Medicine, University of Zagreb, Zagreb, Croatia; Department of Clinical and Molecular Microbiology, Zagreb University Hospital Centre, Zagreb, Croatia
Abstract
Phenotypic detection of metallo-β-lactamases (MBLs) in Acinetobacter (A.) baumannii 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 A. baumannii 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 vs. 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.
Keywords
Beta-lactamases; Imipenem; Meropenem; Acinetobacter baumannii; Edetic acid
Hrčak ID:
220887
URI
Publication date:
1.3.2019.
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