title: The laboratory diagnosis of Pseudomonas aeruginosa that produce metallo-β-lactamases in a Dutch tertiary care centre.
abstract: BACKGROUND
  The laboratory detection of Pseudomonas aeruginosa that produce metallo-β-lactamases (MBLs) is not well defined in regions with a low prevalence of these enzymes. We report a study that developed ethylenediaminetetraacetic acid (EDTA) disk screen tests using doripenem, imipenem and meropenem and investigated the prevalence of these enzymes among clinical isolates of imipenem-resistant P. aeruginosa in Rotterdam during 2008-2009.
  
  
  METHODS
  Using strains with well-characterized β-lactamases and the Clinical and Laboratory Standards Institute (CLSI) disk methodology similar to extended-spectrum β-lactamase (ESBL) detection, inhibition zone diameters were determined in tests with doripenem, imipenem, and meropenem, alone and in combination with 370 μg of EDTA. These tests were compared with the MBL E-test. A positive test was a ≥5 mm increase in zone diameter in the presence of EDTA.
  
  
  RESULTS
  The imipenem EDTA disk screen test showed a sensitivity of 100% and a specificity of 90% in 96 recent clinical isolates. Imipenem in combination with doripenem performed better than imipenem alone, meropenem, and the MBL E-test (sensitivity of 100%; specificity of 95%). The majority of clinical isolates were isolated from patient respiratory specimens. Of the 96 imipenem-resistant P. aeruginosa isolated, 35 (36%) were positive for bla(VIM) genes.
  
  
  CONCLUSIONS
  The EDTA imipenem/doripenem disk test showed accurate and reproducible results with excellent sensitivity and specificity. It is simple to perform and interpret and can be easily introduced into the workflow of a clinical laboratory to screen for MBLs in imipenem-resistant P. aeruginosa. Due to its high specificity the test is also suitable for regions with a low prevalence of these enzymes.
authors.affiliation: Department of Medical Microbiology and Infectious Diseases, Erasmus University Medical Centre, Rotterdam, The Netherlands.
authors.forename: Akke K
authors.initials: AK
authors.lastname: van der Bij
authors.forename: Marco
authors.initials: M
authors.lastname: Mol
authors.forename: Mireille
authors.initials: M
authors.lastname: van Westreenen
authors.forename: Wil H F
authors.initials: WH
authors.lastname: Goessens
authors.forename: Johann D D
authors.initials: JD
authors.lastname: Pitout
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D015780:Carbapenems / Q000494:pharmacology; D052978:Disk Diffusion Antimicrobial Tests / Q000379:methods* / Q000592:standards; D000077726:Doripenem; D004492:Edetic Acid; D006801:Humans; D015378:Imipenem / Q000494:pharmacology; D007753:Laboratories; D000077731:Meropenem; D008826:Microbial Sensitivity Tests; D009426:Netherlands; D011552:Pseudomonas Infections / Q000175:diagnosis / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000145:classification / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D015203:Reproducibility of Results; D013845:Thienamycins / Q000494:pharmacology; D001618:beta-Lactamases / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D015780:Carbapenems; D013845:Thienamycins; D015378:Imipenem; D004492:Edetic Acid; D000077726:Doripenem; D001618:beta-Lactamases; D000077731:Meropenem