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Antimicrobial Agents and Chemotherapy, December 2004, p. 4693-4702, Vol. 48, No. 12
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.12.4693-4702.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Integron Carrying a Novel Metallo-ß-Lactamase Gene, bla_IMP-16, and a Fused Form of Aminoglycoside-Resistant Gene aac(6')-30/aac(6')-Ib': Report from the SENTRY Antimicrobial Surveillance Program

Disciplina de Doenças Infecciosas e Parasitárias, Universidade Federal de São Paulo, São Paulo,¹ Hospital de Base do Distrito Federal, Brasília, Brazil,³ Department of Pathology & Microbiology, University of Bristol, Bristol, United Kingdom,² The JONES Group/JMI Laboratories, North Liberty, Iowa,⁴ Tufts University School of Medicine, Boston, Massachusetts⁵

Received 19 April 2004/ Returned for modification 26 June 2004/ Accepted 4 September 2004

Since January 2002 Pseudomonas sp. strains resistant to carbapenems and ceftazidime have been routinely screened as part of the SENTRY Antimicrobial Surveillance Program for metallo-ß-lactamase production, and their resistance determinants have been analyzed. Pseudomonas aeruginosa index strain 101-4704, which harbors a novel bla_IMP variant, bla_IMP-16, was isolated in April 2002 from a 60-year-old man in Brasília, Brazil. bla_IMP-16 was found on the chromosome of the P. aeruginosa index strain, and the deduced amino acid sequence (IMP-16) showed the greatest identities to IMP-11 (90.3%) and IMP-8 (89.5%). Sequence analysis revealed that bla_IMP-16 was associated with a class 1 integron, which also encoded aminoglycoside-modifying enzymes. Downstream of bla_IMP-16 resided an open reading frame, which consisted of a new aminoglycoside-modifying gene, namely, aac(6')-30, which was fused with aac(6')-Ib'. The amino acid sequence of the aac(6')-30 putative protein showed the most identity (52.7%) to the sequence of AAC(6')-29b described previously. The fourth gene cassette constituted aadA1. The steady-state kinetics of IMP-16 demonstrated that the enzyme preferred cephalosporins and carbapenems to penicillins. The main functional difference observed among the kinetic values for IMP-16 compared to those for other IMPs was a lack of cefoxitin hydrolysis and a lower k_cat/K_m value for imipenem (0.36 µM^–1 · s^–1). This report further emphasizes the spread of metallo-ß-lactamase genes and their close association with various aminoglycoside resistance genes.

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