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

Objectives: The aim of this study was to characterize the different inhibitor-resistant TEM b-lactamases, extended-spectrum b-lactamases (ESBLs) and plasmid-mediated AmpC b-lactamases implicated in b-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, conju-gation, PCR and a sequencing strategy were used to characterize the enzymes. The possible relation-ships between isolates were analysed by PFGE. Results and conclusions: Twenty-five of 1423 isolates were found to display intermediate or full resist-ance to co-amoxiclav, cefotaxime or ceftazidime. Seventeen isolates had reduced susceptibility t