Appearance of aac(6′)-lb-cr gene among extended-spectrum β-lactamase-producing Enterobacteriaceae in a French hospital

Objectives: The aac(6')-lb gene encodes many variants of an aminoglycoside-acetyltra nsferase enzyme that is responsible for amikacin resistance. Recently, a new variant aac(6')-lb-cr capable of modifying aminoglycosides and fluoroquinolones has been described. The aim of our study was to observe the appearance and the location of the aac(6')-lb gene in extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae strains. Methods: Sixty-six and nine non-clonal ESBL-producing Enterobacteriaceae strains were isolated, respectively, for one 3-year period from 1999 to 2001 and one 2-month period in 2005 in a French Hospital (Paris, France). Results: Among these isolates, 35.of them carried the aac(6')-lb gene. Fourteen out of the aac(6')-lb genes of the period 1 and two of the period 2 were genes cassette located within class 1 integrons, whereas 16 and 3, respectively, were outside integrons. One of these encoded an aminoglycoside-acetyltransferase enzyme leading to an acetyltransferase that confers resistance to all aminoglycosides. The new -cr variant of aac(6')-lb was detected in three Escherichia coli isolates in 2005 always associated with CTX-M-15 enzyme. Conclusions: The aac(6')-lb-cr gene, responsible for antibiotic resistance to two very different drugs, is emerging in ESBL-producing Enterobacteriaceae strains isolated in France especially in strains carrying the bla(CTx-M-15) gene. (C) 2008 The British Infection Society. Published by Elsevier Ltd. All rights reserved.