The aminoglycoside 6'-N-acetyltransferases of type Ib (aac(6')-Ib) gene confers resistance to amikacin, tobramycin, kanamycin, and netilmicin but not gentamicin. However, some isolates harboring this gene show reduced susceptibility to amikacin. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) recommends a revision of the phenotypic description for isolates harboring the aac(6')-Ib gene. In this study, we determined the aminoglycoside susceptibility profiles of 58 AAC(6')-Ib-producing Enterobacter cloacae isolates. On the basis of the CLSI and EUCAST breakpoints, a large proportion (84.5% and 55.2%, respectively) of these 58 isolates were found to be susceptible to amikacin. However, among the isolates that were shown to be anikacin-susceptible according to the CLSI and EUCAST breakpoints, only 30.6% and 18.8% isolates, respectively, could be considered to have intermediate resistance on the basis of the EUCAST expert rules. Further studies should be conducted to determine the aminoglycoside susceptibility profiles of aac(6')-Ib-harboring isolates from various geographic regions and to monitor the therapeutic efficacy of amikacin in infections caused by these isolates.
Acetyltransferases/*genetics ; Amikacin/pharmacology ; Aminoglycosides/*pharmacology ; Anti-Bacterial Agents/*pharmacology ; Drug Resistance, Bacterial/genetics ; Enterobacter cloacae/*genetics/isolation & purification ; Enterobacteriaceae Infections/diagnosis/microbiology ; Humans ; Microbial Sensitivity Tests ; Polymerase Chain Reaction ; Sequence Analysis, DNA

OBJECTIVETo explore the distribution of qnr gene and broad spectrum p-lactamase (ESBLs) gene in gram-negative bacteria which were isolated from our hospital patients.

METHODSqnr gene in nonrepetitive 129 isolates of Escherichia coli, 10 isolates of Enterobacter cloacac and 29 isolates of K. pneunoniae were detected by polymerase chain reaction (PCR). For qnr gene positive strains, int I, SHV-1, TEM-1, CTX-M, OXA-I , OXA-II , OXA-III, DHA and EBC genes were examined. Plasmid conjugatable test was applied to examine whether qnr gene was located in conjugate plasmid and ERIC-PCR was carried out for DNA homologous analysis. ESBLs detection (according to phenotypic confirmatory test based on National Committee for Clinical Laboratory Standards criteria) and susceptibility test to 16 antibiotics were also performed.

RESULTSqnr gene was found in 6 clinical isolates including 5 strain of E. coli and one strain of E. cloacac, but qnr gene was undetectable in K. pneunoniae isolates. The 6 clinical isolates were suspectible to imipenem but resistance to some other drugs while only 2 isolates of E. coli were susceptible to quinolone. Among the 6 qnr gene-positive strains, all of them belonged to I type integron-positive isolates, 4 isolates of them were TEM-1 producing strains,with only one isolate was OXA-III gene producing strain, and 2 isolates of them were EBC producing strains. Most of them were with 2 ESBLs gene if not more. qnr gene was on transferable plasmids which could be disseminated by clone.

CONCLUSIONIn Wuhan city, the prevalence of qnr was confirmed. qnr gene were found with some ESBLs gene in the same strains, and qnr gene in suspect strains. The transmission of qnr gene producing strains could be mediated by transferable plasmids or clone, forcing us to make intensive investigation and take effective control measures.

Anti-Bacterial Agents ; pharmacology ; Bacterial Proteins ; genetics ; DNA, Bacterial ; genetics ; Drug Resistance, Bacterial ; genetics ; Enterobacter cloacae ; drug effects ; genetics ; isolation & purification ; Escherichia coli ; drug effects ; genetics ; isolation & purification ; Escherichia coli Proteins ; genetics ; Genes, Bacterial ; Humans ; Imipenem ; pharmacology ; Klebsiella pneumoniae ; drug effects ; genetics ; isolation & purification ; Microbial Sensitivity Tests ; Plasmids ; genetics ; Quinolones ; pharmacology ; Sequence Analysis, DNA ; beta-Lactamases ; genetics