Enterobacteriaceae ; Extended-spectrum β-lactamase ; TEM ; SHV ; Third generation cephalosporins ; Aztreonam
Abstract
Background : Increased isolation of extended-spectrum β -lactamase (ESBL)-producing
Entero bacteriaceae resistant to third generation cephalosporins and aztreonam has been noted
recently. This study was to determine the prevalence of resistance to these drugs and ESBL in
Enterobacteriaceae and to evaluate the methods for de tection.
Methods:During the period of October, 1997 and March, 1998, a total of 731 clinical isolates of
Enterobacteriaceae were collected from patients of the Kosin Medical Center, Pusan, Korea.
Antimicrobial susceptibility test by disk diffusion method and double disk synergy test were
performed. MICs of β -lactams were determined by agar dilution method. And ESBL genotypes
were determined by polymerase chain reaction.
Results: About 10% of Escherichia coli isolates and 20% of Klebsiella pneumoniae isolates were
intermediate or resistant to the third generation cephalosporins or aztreonam. Sensitivities of
cefotaxime, ceftazidime, ceftriaxone and cefpodoxime disks for the detection of ESBL- producing
strains of E. coli and K. pneumoniae by NCCLS standards were 100%, respectively, but that of
aztreonam disk was 97%. Positive predictive value of the ceftazidime disk was higher than those of
other disks. Twenty strains of E. coli, 20 K. pneumoniae, 19 Enterobacter spp., six Citrobacter
freundii, and eight Serratia marcescens showed positive results in double disk synergy test. The
transconjugant strain of K. pneumoniae K20482 had blaSHV, and remains of transconjugants of
ESBL-producing K. pneumoniae, Enterobacter spp. and S. marcescens had blaTEM.
Conclusions: In this study, many strains of Enterobacteriaceae isolated in Korea were resistant
to third generation cephalosporins and aztreonam. Some of the strains of Enterobacter spp. and S.
marcescens as well as E. coli and K. pneumoniae produced ESBL, and majority of these strains had blaTEM. In the detection of ESBL-producing strains of E. coli and K.
pneumoniae by NCCLS standards, all of the antimicrobial agent disks tested were useful, but
ceftazidime disk was most effective because of its highest positive predictive value.