Resistance pattern in gram-negative bacteria causing nosocomial infections and identification of extended spectrum beta-lactamases (ESBL)

Resistance Pattern in Gram-Negative Bacteria Causing Nosocomial Infections and Identification of Extended Spectrum Beta-Lactamases (ESBL) The aim of this study is to search for resistance pattern and existance of extended spectrum beta-lactamase (ESBL), and to find the most appropriate method in identifying ESBL by comparison of combined disc test (CDT), E-test, and double disc synergy test (DDST) in Gram-negative bacteria isolated from specimens of patients who had noso comial infections (NI) in Çukurova University, Faculty of Medicine, Balcali Hospital. The 68 E. coli and 47 Klebsiella spp. strain of nosocomial origin were isolated from 115 specimens of 93 patients between 29.05.2003 and 30.09.2004 in Çukurova Uni versity, Faculty of Medicine, Balcali Hospital Central Laboratory Microbiology Depart ment. Most of the strains (% 53) were isolated from patients who had urinary tract infec tions (UTI). The sensitvity of these nosocomial strains were detected by disc diffusion test (DDT). Altough there was a general resistance against trimethoprim/sulfomethoxasol, third generation cepholosporins and aztreonam, the least resistance was against imipenem. In this study, isolates that found to be suspicous for ESBL against ceftazidime, ceftriaxone, cefotaxime, and aztreonam by DDT were also studied by DDST, CDT and E- test ESBL test and after the confirmation of positivity, the tests were compared. ESBL positivity among Klebsiella spp. was detected in 30 of 47 strains (63.8 %) by E-test, 27 (57.44 %) by DDST, 21 (44.68 %) by CDT. Among E. coli strains, ESBL positivity was found in 42 of 68 (61.76 %) strains by E-test, 36 (52.54 %) by DDST, 34 (50 %) by CDT. Of 60 strains found to be ESBL negative by CDT, which is accepted as the referance test for identification of ESBL, 18 strains by DDT, 17 strains by E-test, 8 strains by DDST were detected ESBL positive. Consequently, as DDT and E-test have a higher false positivity than DDST, and besides in E-test the difficulty in evaluation of the results in which clavulanic acid occasionally diffuses over the site of beta-lactam antibiotic and its high cost, CDT and DDST would be preferred for detection of ESBL because of their practical use and low cost. Key words: ESBL, E. coli, Klebsiella spp., combined disc test, nosocomial infection. IX