Evaluation of a new meropenem–EDTA double-ended Etest strip for the detection of the CfiA metallo-b-lactamase in clinical isolates of Bacteroides fragilis
P. Bogaerts1, A. Engelhardt2, C. Berhin1, L. Bylund2, P. Ho2, A. Yusof 2 and Y. Glupczynski1
Laboratory of Bacteriology, UCL-MontGodinne, Universite´ catholique de Louvain, Yvoir, Belgium and 2 AB BIODISK, Solna, Sweden
Thirty-five Bacteroides fragilis clinical isolates with
varying susceptibility to meropenem were analysed with a prototype of a double-ended Etest strip containing meropenem ± EDTA, designed for the detection of the CfiA metallo-b-lactamase. Phenotypic results obtained with this new Etest strip were related to the genotype and compared to the results of the Etest containing imipenem ± EDTA.
Whereas the Etest with imipenem ± EDTA only allowed detection of isolates with high-level resistance (both MICs of imipenem and meropenem >32 mg ⁄ L), reflecting the possible underestimation of CfiA prevalence in B. fragilis, the Etest with meropenem ± EDTA proved to be more accurate, particularly for isolates with low-level carbapenem resistance, suggesting its potential for broader detection of CfiA production.
Keywords Bacteroides, Etest, metallo-b-lactamase, phenotypic detection
Original Submission: 27 December 2007;
Revised Submission: 9 April 2008;
Accepted: 19 May 2008
Edited by E. Collatz
Clin Microbiol Infect 2008; 14: 973–977
10.1111/j.1469-0691.2008.02065.x
Bacteroides fragilis is an important anaerobic pathogen commonly associated with polymicrobial
infections. Carbapenems are normally highly active against B. fragilis. However, carbapenemresistant B. fragilis isolates have been reported [1–15], mainly because of the production of CfiA, a class B metallo-b-lactamase (MBL) present in up to 7% of those isolates [3,4]. This enzyme is usually poorly expressed, but the insertion of a variety of insertion sequence (IS) elements upstream of cfiA, subsequent to a single genetic event selected with carbapenems [11,16], switches on gene expression and leads to high-level carbapenem resistance [4,5,11–16]. Thus, it is important to detect all B. fragilis isolates that harbour the cfiA gene in order to avoid inappropriate carbapenem usage, which may result in the selection and emergence of high-level resistance in these strains. In that respect, enzymatic studies of CfiA [17] have shown that meropenem is a better substrate than imipenem for this MBL of B. fragilis.
The aim of this preliminary study was to assess the potential value of a novel Etest strip containing meropenem ± EDTA to detect carbapenem resistance due to CfiA in B. fragilis.
