Background: Extended-spectrum b-lactamase (ESBL)-producing strains of Klebsiella pneumoniae have caused major therapeutic problems worldwide since the majority are resistant to various antibiotics. In this study, an investigation was conducted regarding antibiotic-resistant patterns of 128 isolates of K. pneumoniae cultured from Iranian patients at two teaching hospitals during 2004-2005.
Material/Methods: The susceptibility of isolates to 21 antimicrobial agents was determined using the disk diffusion method. Disks containing ceftazidime, cefotaxime, ceftazidime/clavulanic acid, and cefotaxime/clavulanic
acid were used in the phenotypic confi rmatory (PCT) method to detect ESBL isolates. A comparison between the confi rmatory method and double-disk synergy test (aztreonam, ceftazidime, ceftriaxone, cefotaxime, and amoxicillin/clavulanic acid) was also made to assign the appropriate
method of detection for ESBLs. The E-test was used to determine the susceptibility of isolates to cefepime.
Results: All strains were susceptible to imipenem and meropenem. Resistance to ciprofl oxacin and gentamicin were found in 37% (n=47) and 33% (n=42) of isolates, respectively. Production of ESBL was detected in 44.5% of isolates. Resistance to cefepime was found in 40% of isolates.
Conclusions: The prevalence of ESBL strains in the study hospitals is high. The double-disk synergy method is not preferable in successfully detecting ESBL strains. More importantly, 33% of ESBL strains were also resistant to ciprofl oxacin and aminoglycosides. Based on the laboratory results, it is recommended that prescription of cephalosporins be restricted to susceptible isolates and that the usage of other effective antibiotics be considered.

Keywords: Anti-Infective Agents - pharmacology, Cephalosporins - pharmacology, Ciprofloxacin - pharmacology, Drug Evaluation, Preclinical, Drug Resistance, Bacterial, Gentamicins - pharmacology, Imipenem - pharmacology, Iran, Klebsiella pneumoniae - metabolism, Thienamycins - pharmacology, beta-Lactamases - metabolism