JAC Advance Access published online on May 2, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn185
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Original research |
A convenient microbiological assay employing cell-free extracts for the rapid characterization of Gram-negative carbapenemase producers
,*1 Departamento de Microbiología, Instituto de Biología Molecular y Celular de Rosario (IBR), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, 2000 Rosario, Argentina 2 Hospital Intendente Carrasco, Departamento Bioquímico Municipal, Secretaría de Salud Pública, Municipalidad de Rosario, 2000 Rosario, Argentina 3 Departamento de Química Biológica, Instituto de Biología Molecular y Celular de Rosario (IBR), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, 2000 Rosario, Argentina
Received 16 November 2007; returned 4 January 2008; revised 31 March 2008; accepted 2 April 2008
* Corresponding author. Tel: +54-341-4350661; Fax: +54-341-4390465; E-mail: limansky{at}ibr.gov.ar
Objectives: The dissemination of metallo and serine carbapenem-hydrolysing β-lactamases among Gram-negative nosocomial bacteria represents an acute problem worldwide. Here, we present a rapid and sensitive assay for the characterization of carbapenemase producers to aid in infection control and prevention.
Methods: The assay involves a rapid disruption of bacterial isolates with silicon dioxide microbeads, followed by the testing in cell-free extracts of hydrolytic activity towards various β-lactams including two carbapenems (imipenem and meropenem) and a cephalosporin (ceftazidime). A parallel testing of the effects of selective β-lactamase inhibitors such as EDTA and clavulanic acid allows differentiation of metallo carbapenemases from serine carbapenemases, and also clavulanic-acid-sensitive from -resistant enzymes among the latter.
Results: The efficiency of bacterial disruption using silicon dioxide microbeads was identical to that of ultrasonic treatment. The subsequent microbiological assay aimed to evaluate both substrate specificity and inhibitor profile of carbapenem-hydrolysing enzymes present in the extracts and allowed an accurate differentiation of A, B and D types, as judged by the analysis of 24 well-characterized clinical strains that included metallo-β-lactamase producers (i.e. VIM-, IMP- and SPM-type Pseudomonas producers; an L1 Stenotrophomonas maltophilia producer; and a GOB-18 Elizabethkingia meningoseptica producer) as well as serine carbapenemase producers (i.e. an SME-type Serratia marcescens producer, a GES-2 Pseudomonas aeruginosa producer, Klebsiella pneumoniae and Citrobacter freundii KPC-2 producers and OXA-type Acinetobacter baumannii producers).
Conclusions: We have developed a convenient microbiological assay aimed to more accurately and in a short time characterize carbapenem-hydrolysing enzymes produced by Gram-negative bacteria. The assay possesses broad applicability in the clinical setting.
Key Words: carbapenem resistance , β-lactamase detection , bacterial disruption
These authors contributed equally to this work.
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