Characterisation of a novel AmpC beta-lactamase, DHA-33, resistant to inhibition by cloxacillin.

Jacqueline Findlay, Laurent Poirel, Abdessalam Cherkaoui, Jacques Schrenzel, Patrice Nordmann

Diagnostic microbiology and infectious disease 2024 Aug

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Plasmid-encoded DHA-type AmpCs have been extensively reported in Enterobacterales. The expression of the genes encoding these plasmid-mediated enzymes are inducible and these enzymes are capable of conferring resistance to a wide spectrum of beta-lactams including penicillins and broad-spectrum cephalosporins. The identification of infections caused by AmpC-producing bacteria is a necessity, both for infection control/epidemiology purposes and to inform treatment choices. A common testing method for AmpC production in the clinical laboratory setting is to supplement Mueller-Hinton agar plates used for antibiotic disk diffusion with cloxacillin, a potent inhibitor of AmpC enzymes. Here we describe a novel DHA variant, produced by a clinical Escherichia coli isolate, which is resistant to cloxacillin inhibition. Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.

Citation

Jacqueline Findlay, Laurent Poirel, Abdessalam Cherkaoui, Jacques Schrenzel, Patrice Nordmann. Characterisation of a novel AmpC beta-lactamase, DHA-33, resistant to inhibition by cloxacillin. Diagnostic microbiology and infectious disease. 2024 Aug;109(4):116356