Prevalence of aac(6')-Ib-cr in clinical isolates of Klebsiella pneumoniae

Abstract

Objective To investigate the prevalence of aac(6')-Ib-cr in clinical isolates of Klebsiella pneumoniae.Methods A total of 337 isolates of Klebsiella pneumoniae were isolated from clinical specimens in our hospital from Jan,2006 to Sep,2007.Gentamycin,amikacin or tobramicin was used to screen the isolated with aac(6')-Ib-cr.aac(6')-Ib and class 1 interase gene(intl1)was determined by PcR All PCR products of aac(6')-Ib were sequenced for determination of aac(6')-Ib-cr. MICs of antibiotics were determined by agar dilution method.The ESBLs-producing isolates were determined by the CLSI-recommended confirmatory tests.Conjugation test was used to detect the transfer of plasmid.Results Of the 337 clinical isolates of Klebsiella pneumoniae,64(19.0%),28(8.3%)and 55(16.3%)isolates were resistant to gentamycin,amikacin and tobramycin,respectively.Among 64 gentamycin-resistant isolates,24(37.5%)were positive for aac(6')-Ib-cr,including 13 ciprofloxacin-resistant isolates and 11 ciprofloxacinsusceptible isolates.The prevalence of aac(6')-Ib-cr in ciprofloxacin-resistant and-susceptible isolates were 54.2%(13/24)and 27.5%(11/40).The positive rates of ESBLs and intl1 in the 24 isolates carrying aac(6')-Ib-cr were 79.2%(19/24)and 91.7%(22/24).Plasmids carrying aac(6')-Ib-cr of 13 isolates were successfully transferred to E.coli J53.Plasmids of all transconjugants were positive for aac(6')-Ib-cr and intl1.All transconjugants were ESBL producing strains.Conclusions aac(6')-Ib-cr exists widely in clinical isolates of Klebsiella pneumoniae.aac(6')-Ib-cr and ESBL gene usually coexist in a selftransmissible conjugative plasmid by class 1 integron. Key words: Klebsiella pneumoniae; Acetyltransferases; beta-Lactamases; Integrons