title: Sensitive EDTA-based microbiological assays for detection of metallo-{beta}-lactamases in nonfermentative gram-negative bacteria.
abstract: The worldwide spread of metallo-beta-lactamase (MBL)-producing gram-negative bacilli represents a great concern nowadays. Sensitive assays for their specific detection are increasingly demanded to aid infection control and to prevent their dissemination. We have developed a novel microbiological assay employing crude bacterial extracts, designated EDTA-imipenem microbiological assay (EIM), to identify MBLs in nonfermentative gram-negative clinical strains. We also evaluated the ability of EIM to detect MBLs in comparison to those of other currently employed screening methods, such as the EDTA disk synergy test (EDS) with imipenem as a substrate and the Etest method. The sensitivities of EIM and Etest were similar (1 versus 0.92, respectively) and much higher than that of EDS (0.67). Moreover, both EIM and Etest displayed the maximum specificity. Modifications were introduced to EDS, including the simultaneous testing of three different beta-lactams (imipenem, meropenem, and ceftazidime) and two different EDTA concentrations. This resulted in a sensitivity improvement (0.92), albeit at a cost to its specificity. A simple strategy to accurately detect MBL producers is proposed; this strategy combines (i) an initial screening of the isolates by the extended EDS assay to select the potential candidates and (ii) confirmation of the true presence of MBL activity by EIM.
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario, Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, 2000 Rosario, Argentina.
authors.forename: Patricia
authors.initials: P
authors.lastname: Marchiaro
authors.forename: María A
authors.initials: MA
authors.lastname: Mussi
authors.forename: Viviana
authors.initials: V
authors.lastname: Ballerini
authors.forename: Fernando
authors.initials: F
authors.lastname: Pasteran
authors.forename: Alejandro M
authors.initials: AM
authors.lastname: Viale
authors.forename: Alejandro J
authors.initials: AJ
authors.lastname: Vila
authors.forename: Adriana S
authors.initials: AS
authors.lastname: Limansky
mesh_terms: D001431:Bacteriological Techniques / Q000379:methods*; D004492:Edetic Acid; D004926:Escherichia coli; D005069:Evaluation Studies as Topic; D006090:Gram-Negative Bacteria / Q000201:enzymology / Q000302:isolation & purification*; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D006801:Humans; D015378:Imipenem; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D001618:beta-Lactamases / Q000032:analysis*
chemical_list: D015378:Imipenem; D004492:Edetic Acid; D001618:beta-Lactamases