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Antimicrobial Agents and Chemotherapy, February 2006, p. 618-624, Vol. 50, No. 2
0066-4804/06/$08.00+0     doi:10.1128/AAC.50.2.618-624.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

CMY-16, a Novel Acquired AmpC-Type ß-Lactamase of the CMY/LAT Lineage in Multifocal Monophyletic Isolates of Proteus mirabilis from Northern Italy

Dipartimento di Biologia Molecolare, Laboratorio di Fisiologia e Biotecnologia dei Microrganismi, Università di Siena, I-53100 Siena,¹ Dipartimento di Scienze Morfologiche Eidologiche e Cliniche, Sezione di Microbiologia, Università di Pavia, I-27100 Pavia,² Laboratorio di Microbiologia, Ospedale di Circolo, Università dell'Insubria, I-21100 Varese,³ Ospedali Riuniti, I-24128 Bergamo,⁴ Ospedale Maggiore, I-28100 Novara, Italy⁵

Received 21 July 2005/ Returned for modification 7 September 2005/ Accepted 17 November 2005

We report multifocal detection (four different cities in northern Italy) of Proteus mirabilis isolates resistant to both oxyimino- and 7--methoxy-cephalosporins and producing a novel acquired AmpC-like ß-lactamase. The enzyme, named CMY-16, is a variant of the CMY/LAT lineage, which differs from the closest homologues, CMY-4 and CMY-12, by a single amino acid substitution (A171S or N363S, respectively) and from CMY-2 by two substitutions (A171S and W221R). Expression of the cloned bla_CMY-16 gene in Escherichia coli decreased susceptibility to penicillins, cephalosporins, and aztreonam. Tazobactam was more effective than clavulanate at antagonizing the enzyme activity. Genotyping, by random amplification of polymorphic DNA and pulsed-field gel electrophoresis of genomic DNA digested with SfiI, showed that isolates were clonally related to each other, although not identical. The bla_CMY-16 gene was not transferable to E. coli by conjugation or transformation. In all isolates, it was chromosomally located and inserted in a conserved genetic environment. PCR mapping experiments revealed that the bla_CMY-16 was flanked by ISEcp1 and the blc gene, similar to other genes of this lineage from plasmids of Salmonella enterica, Klebsiella spp., and E. coli. Overall, these results revealed multifocal spreading of a CMY-16-producing P. mirabilis clone in northern Italy. This finding represents the first report of an acquired AmpC-like ß-lactamase in Proteus mirabilis from Italy and underscores the emergence of similar resistance determinants in the European setting.

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