Dissemination of transferable CTX-M-type extended-spectrum beta-lactamase-producing Escherichia coli in Korea.
OBJECTIVE
Among 365 Escherichia coli isolated in 2003, 31 cefotaxime-resistant isolates were obtained from clinical specimens taken from adults hospitalized in Busan, Korea. Six extended-spectrum beta-lactamase (ESBL)-producing isolates were investigated further to determine the mechanism of resistance.


RESULTS
These isolates were analysed by antibiotic susceptibility testing, pI determination, plasmid profiles, transconjugation test, PCR-restriction fragment length polymorphism (RFLP), enterobacterial repetitive consensus (ERIC)-PCR and DNA sequencing. All six of these isolates were found to contain the CTX-M-type ESBL genes. Five clinical isolates and their transconjugants produced CTX-M-3. One clinical isolate (K17391) and its transconjugant (trcK17391) produced CTX-M-15. Five clinical isolates also produced another TEM-1. One clinical isolate (K12776) also contained another TEM-52. CTX-M-3 ESBL gene was responsible for the resistance to piperacillin, cephalothin, cefotaxime, cefepime and aztreonam. CTX-M-15 or TEM-52 was especially responsible for the resistance to ceftazidime.


CONCLUSIONS
These results appear to represent the in vivo evolution of CTX-M-type beta-lactamase genes (bla(CTX-M-3) --> bla(CTX-M-15)) under the selective pressure of antimicrobial therapy (especially ceftazidime). PCR-RFLP is a reliable method to discriminate CTX-M-15 gene from CTX-M-3 gene. ERIC-PCR analysis revealed that dissemination of CTX-M-3 was not due to a clonal outbreak of a resistant strain but to the intra-species spread of resistance to piperacillin, cephalothin, cefotaxime, cefepime and aztreonam in Korea.


CONCLUSIONS
This is the first report of the occurrence of CTX-M-1 cluster ESBLs in Korea. A more comprehensive survey of these ESBL types from Korea is urgently needed because of the in vivo evolution of CTX-M-15 from CTX-M-3. The emergence of these CTX-M-type ESBLs suggests that diagnostic laboratories should screen for ESBLs with ceftazidime as well as cefotaxime; they should still perform clavulanate synergy tests on resistant isolates.
Jeong
S H
SH
Department of Laboratory Medicine and Graduate School of Public Health, Kosin University College of Medicine, Busan, Republic of Korea.
Bae
I K
IK
Kwon
S B
SB
Lee
J H
JH
Song
J S
JS
Jung
H I
HI
Sung
K H
KH
Jang
S J
SJ
Lee
S H
SH
D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001483:Base Sequence; D002439:Cefotaxime / Q000494:pharmacology*; D018550:Cephalosporin Resistance / Q000235:genetics*; D003227:Conjugation, Genetic / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D005798:Genes, Bacterial / Q000235:genetics; D006801:Humans; D007525:Isoelectric Focusing / Q000379:methods; D007723:Korea; D008826:Microbial Sensitivity Tests / Q000379:methods; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction / Q000379:methods; D012150:Polymorphism, Restriction Fragment Length; D001618:beta-Lactamases / Q000235:genetics*
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; C055184:beta-lactamase TEM-3; D001618:beta-Lactamases; D002439:Cefotaxime