Appearance of aac(6')-Ib-cr gene among extended-spectrum beta-lactamase-producing Enterobacteriaceae in a French hospital.

OBJECTIVES: The aac(6')-Ib gene encodes many variants of an aminoglycoside-acetyltransferase enzyme that is responsible for amikacin resistance. Recently, a new variant aac(6')-Ib-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')-Ib 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')-Ib gene. Fourteen out of the aac(6')-Ib 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')-Ib was detected in three Escherichia coli isolates in 2005 always associated with CTX-M-15 enzyme.

CONCLUSIONS: The aac(6')-Ib-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.