Antibiotic resistance mechanisms of Escherichia coli Isolates from urinary specimens.
BACKGROUND
This study was designed to characterize urinary isolates of Escherichia coli that produce extended-spectrum beta-lactamases (ESBLs) and to determine the prevalence of other antimicrobial resistance genes.


METHODS
A total of 264 non-duplicate clinical isolates of E. coli were recovered from urine specimens in a tertiary-care hospital in Busan in 2005. Antimicrobial susceptibility was determined by disk diffusion and agar dilution methods, ESBL production was confirmed using the double-disk synergy (DDS) test, and antimicrobial resistance genes were detected by direct sequencing of PCR amplification products. E. coli isolates were classified into four phylogenetic biotypes according to the presence of chuA, yjaA, and TSPE4.


RESULTS
DDS testing detected ESBLs in 27 (10.2%) of the 264 isolates. The most common type of ESBL was CTX-M-15 (N=14), followed by CTX-M-3 (N=8) and CTX-M-14 (N=6). All of the ESBL-producing isolates were resistant to ciprofloxacin. PCR experiments detected genes encoding DHA-1 and CMY-10 AmpC beta-lactamases in one and two isolates, respectively. Also isolated were 5 isolates harboring 16S rRNA methylases, 2 isolates harboring Qnr, and 19 isolates harboring AAC(6')-Ib-cr. Most ESBL-producing isolates clustered within phylogenetic groups B2 (N=14) and D (N=7).


CONCLUSIONS
CTX-M enzymes were the dominant type of ESBLs in urinary isolates of E. coli, and ESBL-producing isolates frequently contained other antimicrobial resistance genes. More than half of the urinary E. coli isolates harboring CTX-M enzymes were within the phylogenetic group B2.
Song
Sungwook
S
Department of Laboratory Medicine and Research Institute of Bacterial Resistance, Yonsei University College of Medicine, Seoul, Korea.
Lee
Eun Young
EY
Koh
Eun-Mi
EM
Ha
Ho Sung
HS
Jeong
Ho Joong
HJ
Bae
Il Kwon
IK
Jeong
Seok Hoon
SH
D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D001437:Bacteriuria / Q000382:microbiology; D002939:Ciprofloxacin / Q000494:pharmacology; D052978:Disk Diffusion Antimicrobial Tests; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology / Q000302:isolation & purification; D006801:Humans; D008780:Methyltransferases / Q000235:genetics; D010802:Phylogeny; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics*
D001426:Bacterial Proteins; D002939:Ciprofloxacin; C446079:16S rRNA - m7G methyltransferase; D008780:Methyltransferases; C048795:AmpC beta-lactamases; D001618:beta-Lactamases