Detection and typing of extended-spectrum beta-lactamases in clinical isolates of the family Enterobacteriaceae in a medical center in Turkey

To determine and type the extended-spectrum beta -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 presumptiv ely defined as ESBL producers according to the result of disk method using ESBL marker antibiotics (aztreonam, ceftazidime, and cefoxitin). These 80 s trains were retested with the double-disk synergy test (DDST), the E-test E SBL strip, a 5-mug ceftazidime disk, and agar dilution MICs of ceftazidime with and without clavulonic acid. Isoelectric focusing was performed to con firm ESBL production and type the beta -lactamases. By evaluation of the re sults of all tests used for ESBL detection together with isoelectric focusi ng, 33 (4.9%) of the 668 isolates were described as ESBL producer. The posi tive results of the agar dilution test, DDST, the E-test strip, and 5-mug c eftazidime disk were 32, 26, 27, and 26 of the 33 strains, respectively. ES BL 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 ES BL 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-derive d (pI 7.6) ESBL expression among the isolates of the family Enterobacteriac eae is an important problem in our medical center.