Journal Article

Disc diffusion-based screening tests for extended-spectrum β-lactamases in <i>Haemophilus influenzae</i>

Stephen G. Tristram, Bülent Bozdogan and Peter C. Appelbaum

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 55, issue 4, pages 570-573
Published in print April 2005 | ISSN: 0305-7453
Published online April 2005 | e-ISSN: 1460-2091 | DOI: http://dx.doi.org/10.1093/jac/dki036
Disc diffusion-based screening tests for extended-spectrum β-lactamases in Haemophilus influenzae

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  • Medical Oncology
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Objectives: To establish a suitable screening test for the detection of extended-spectrum β-lactamases (ESBLs) in Haemophilus influenzae.

Methods: Double disc diffusion tests using cephalosporin discs adjacent to an amoxicillin/clavulanate 3 μg disc, prediffusion tests, where an amoxicillin/clavulanate 3 μg disc was prediffused before being replaced with a cephalosporin disc, and combination cephalosporin/clavulanate discs were used to screen recombinant H. influenzae expressing cloned ESBLs. Methods initially determined to be suitable were validated by testing a range of clinical strains.

Results: Enhanced zones around cephalosporin discs due to synergy with an adjacent amoxicillin/clavulanate disc were not reliably demonstrated with the recombinant H. influenzae strains expressing ESBLs. Cefotaxime 5 μg or 30 μg and cefpodoxime 10 μg discs prediffused with an amoxicillin/clavulanate 3 μg disc, and cefotaxime 30 μg/clavulanate 10 μg and cefpodoxime 10 μg/clavulanate 1 μg combination discs all gave zone sizes ≥ 5 mm greater than the corresponding plain disc for all recombinant ESBL-producing strains. None of the clinical strains gave enhanced zones.

Conclusions: Cefotaxime 5 or 30 μg or cefpodoxime 10 μg discs prediffused with an amoxicillin/clavulanate 3 μg disc, or cefotaxime 30 μg/clavulanate 10 μg and cefpodoxime 10 μg/clavulanate 1 μg combination discs are all suitable for screening H. influenzae isolates for the presence of ESBLs. ESBL-producing strains should show an increase in zone diameter of ≥ 5 mm compared with the corresponding plain cephalosporin disc.

Keywords: H. influenzae; ESBLs; TEM

Journal Article.  1804 words. 

Subjects: Medical Oncology ; Critical Care

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