Abstract
To determine and type the extended-spectrum β-lactamases (ESBLs) among the family Enterobacteriaceae in a medical center, a total of 668 clinical isolates were screened. Of the 668 isolates, the 80
strains were presumptively defined as ESBL producers according to the result of disk method using ESBL marker antibiotics (aztreonam, ceftazidime, and cefoxitin). These 80 strains were retested with the
double-disk synergy test (DDST), the E-test ESBL strip, a 5-µg ceftazidime disk, and agar dilution MICs of ceftazidime with and without clavulonic acid. Isoelectric focusing was performed to confirm
ESBL production and type the β-lactamases. By evaluation of the results of all tests used for ESBL detection together with isoelectric focusing, 33 (4.9%) of the 668 isolates were described as ESBL
producer. The positive results of the agar dilution test, DDST, the E-test strip, and 5-µg ceftazidime disk were 32, 26, 27, and 26 of the 33 strains, respectively. ESBL positivity was 48.8% in
Klebsiella
species, 15.4% in
Citrobacter
species, 4.9% in
Enterobacter
species and 1.1% in
Escherichia coli
strains. The ESBL enzymes frequently determined were SHV-2/6-like (pI 7.6), SHV-5-like
(pI 8.2), SHV-4-like (pI 7.8), and SHV-3-like (pI 7). SHV-derived enzymes were commonly observed in
Klebsiella
spp whereas TEM-related enzymes were seen in
E. coli
strains. The results of
this study indicated that SHV-2/6-derived (pI 7.6) ESBL expression among the isolates of the family Enterobacteriaceae is an important problem in our medical center.