prevalence of extended-spectrum beta lactamase positive and multidrug resistance pattern of escherichia coli and klebsiella pneumoniae isolates, semnan, iran

background and objectives: β-lactamase production is the predominant mechanism for resistance to β-lactams in enterobacteriaceae. the producing isolates are often multidrug resistant and are major hosts for extended spectrum β-lactamases. this study was designed to determine the prevalence of extended-spectrum β-lactamase producing isolates of escherichia coli and klebsiella pneumoniae and their antibiotic resistance patterns in semnan, iran. materials and methods: 275 escherichia coli and 107 k. pneumoniae isolates from clinical specimens were investigated. combined disk test was used as a screening test for esbl production. disk diffusion test was performed for antibiotic susceptibility testing. results: the greatest resistance was observed against ampicillin (96.3%) and the least resistance was against ceftazidime (16.5%). using combined disks as phenotypic confirmatory test, esbl were detected among 69 (18.1%) of all isolates. frequency of esbl production was 17.45% and 19.6% for e. coli and k. pneumoniae respectively. conclusion: high levels of resistance and esbl production found in the e. coli and k. pneumoniae in this study make the choice of empirical antibiotic regimens difficult. antimicrobial susceptibility testing and esbl production monitoring are recommended in patients