Characteristics of aac(6')-Ib-cr gene in extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae isolated from Chungnam area.
BACKGROUND
Concomitant quinolone resistance in extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae is a crucial problem in the clinical management of infections. In foreign countries, the fluoroquinolone acetylating aminoglycoside-(6)-N-acetyltransferase (aac[6']-Ib-cr) gene, a novel plasmid-mediated quinolone resistance determinant has been reported to occur in conjunction with qnr. We aim to investigate the prevalence and characteristics of concomitant aac(6')-Ib-cr and qnr expression in ESBL-producing Escherichia coli and Klebsiella pneumoniae in Korea.


METHODS
Between December 2007 and April 2008, we collected 60 and 69 clonally unrelated non-repetitive clinical isolates of ESBL-producing E. coli and K. pneumoniae, respectively. We studied the expressions of 11 types of ESBL-encoding genes, 4 types of 16s rRNA methylase genes; rmtA, rmtB, rmtC and armA, 3 types of qnr genes; qnrA, qnrB, qnrS and aac(6')-Ib. The presence of aac(6')-Ib-cr variants was detected by sequencing. The involvement of integrons was studied using multiplex PCR and sequencing of gene-cassette arrays. Conjugation experiments were performed to confirm plasmid-mediated resistance and the relationships among co-harbored genes.


RESULTS
We observed a high prevalence of the cr variant (61.1%) of aac(6')-Ib, and the prevalence of this variant in qnr and aac(6')-Ib-co-harboring isolates (67.4%) was higher than in qnr-negative isolates (51.7%). The high prevalence of the cr variant was significantly related to the high minimum inhibitory concentrations (MICs) of ciprofloxacin, tobramycin, and amikacin and indicated the statistically significant roles of qnrB, qnrS, rmtA, and rmtB in quinolone and aminoglycoside resistance.


CONCLUSIONS
The aac(6')-Ib-cr variants were widespread and showed significant relation to the high-level quinolone and aminoglycoside resistance in ESBL-producing E. coli and K. pneumoniae.
Shin
So Youn
SY
Department of Laboratory Medicine, Chungnam National University College of Medicine, Daejeon, Korea.
Kwon
Kye Chul
KC
Park
Jong Woo
JW
Song
Jeong Hoon
JH
Ko
Young Hyun
YH
Sung
Ji Youn
JY
Shin
Hae Won
HW
Koo
Sun Hoe
SH
D000123:Acetyltransferases / Q000235:genetics*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005798:Genes, Bacterial / Q000235:genetics; D007711:Klebsiella pneumoniae / Q000201:enzymology / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D056910:Republic of Korea; D017422:Sequence Analysis, DNA; D001618:beta-Lactamases / Q000096:biosynthesis*
D000123:Acetyltransferases; C056532:aminoglycoside N(6')-acetyltransferase; D001618:beta-Lactamases