Increase in β-lactam-resistant Proteus mirabilis strains due to CTX-M- and CMY-type as well as new VEB- and inhibitor-resistant TEM-type β-lactamases

Objectives: The aim of this study was to characterize the different inhibitor-resistant TEM β-lactamases, extended-spectrum β-lactamases (ESBLs) and plasmid-mediated AmpC β-lactamases implicated in β-lactam resistance in Proteus mirabilis, which has increased over recent years. Methods: From February 2000 to December 2005, 1423 clinical isolates of P. mirabilis were collected. The AmpC phenotype was checked by means of a double-disc synergy test using cloxacillin as an inhibitor of AmpC enzymes. The production of ESBL was assessed by the double-disc synergy method and by Etest ESBL. Analytical isoelectric focusing, determination of kinetic constants, conjugation, PCR and a sequencing strategy were used to characterize the enzymes. The possible relationships between isolates were analysed by PFGE. Results and conclusions: Twenty-five of 1423 isolates were found to display intermediate or full resistance to co-amoxiclav, cefotaxime or ceftazidime. Seventeen isolates had reduced susceptibility to co-amoxiclav; of these, seven produced TEM-110, eight produced the new TEM-159, one the new TEM-160 and one TEM-1. Five isolates producing TEM-110, TEM-159 or TEM-160 enzymes shared the same PFGE profile. Three isolates produced an ESBL, CTX-M-1, CTX-M-32 and the new variant, VEB-4. Finally, five isolates with an AmpC phenotype produced CMY-2, two with the same PFGE profile. Our data emphasize the diversity of β-lactamases found in this species. © The Author 2008. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.