Prevalence of the fluoroquinolone-modifying acetyltransferase gene aac(6')-ib-cr among extended-spectrum betalactamase-producing enterobacterial isolates in a cancer hospital in bulgaria

Objectives: To determine the prevalence of the fluoroquinolonemodifying aminoglycoside acetyltransferase-encoding gene aac(6')-Ib-cr among enterobacterial isolates carrying extendedspectrum beta-lactamases (ESBLs). Methods: One hundred and sixty three non-duplicate, clinically relevant ESBL-producing enterobacterial isolates collected between 2000 and 2005 were screened for aac(6')-Ib by PCR. aac(6')-Ib-cr was identified by sequencing. PCR amplification and DNA sequencing identified betalactamase genes in all aac(6')-Ib-cr-positive isolates. Pulsed-field gel electrophoresis (PFGE) was used to investigate the clonality of aac(6')-Ib-cr-carrying isolates. Results: Ninety-nine of 163 ESBLproducing isolates (60.7%) were positive for aac(6')-Ib including Escherichia coli (65/94), Klebsiella pneumoniae (21/40), Citrobacter freundii (7/10), Enterobacter cloacae (1/7), Klebsiella oxytoca (1/2) and single isolates of Enterobacter aerogenes, Morganella morganii, Providencia rettgeri and Escherichia hermannii. The aac(6')-Ib-cr variant was identified in 52 (31.9% of all) isolates including 47 E. coli, 2 C. freundii, and 1 each of K. pneumoniae, E. aerogenes and M. morganii. Among the aac(6')-Ib-cr-positive isolates, 32 had bla_CTXM-15, bla_OXA-1 and bla _TEM-1, 16 had bla_CTX-M-15 and bla_OXA-1, and 2 had bla_CTX-M-15, bla_OXA-1, bla_SHV-12 and bla_TEM-1. The remaining 2 isolates had bla_TEM-1 and ESBL of none of the studied types. PFGE of 47 E. coli digests displayed 30 different patterns, suggesting the limited importance of clonal spread of aac(6')-Ib-cr gene. Conclusions: The aac(6')-Ib-cr variant was present in various species in the family Enterobacteriaceae and highly prevalent in E. coli isolates (50%). The majority of aac(6')-Ib-cr-carrying isolates co-produced _CTX-M-15 and OXA-1 beta-lactamases. The spread of multiresistant isolates expressing the aminoglycoside-and fluoroquinolonemodifying enzyme AAC(6')-Ib-cr together with ESBLs is a worrisome development requiring continuous monitoring.