detection of ctx-m-β lactamases form isolated klebsiella pneumoniae

background and objective: organisms producing ctx-m β-lactamases are emerging as a source of resistance to oxyiminocefalosporins such as ceftriaxone and ceftazidime. however, the laboratory detection of these strains is not well defined. in this study, phenotypic assay for screening of extended-spectrum β-lactamases producing strains and molecular assay for the identification of ctx-m β-lactamases genes was developed and used to investigate the prevalence of these enzymes among clinical isolates of klebsiella pneumoniae in three general hospitals of tehran, iran. materials and methods: phenotypic detection was used for screening of isolates by agar dilution method. a decrease of ≥3 doubling dilution in an mic for either ceftriaxone or ceftazidime tested in combination with 4 mg/l clavulanic acid (prepared from glasco smith company) versus its mic when tested alone, confirmed an esbl-producing organism. the pcr assay consisted of four primer sets. results: in initial screening test, 117 (69%) from 168 clinical isolates were positive and 51 isolates (31%) were negative. from the positive isolates, 96 isolates were positive in phenotypic confirmatory test. using molecular assay, 117 strains potentially producing extended-spectrum-β-lactamases were examined for the presence of ctx-m enzymes: 88 strains (75.2%) were positive for blactx-m group і genes, 1 strain (0.85%) was positive for blactx-m group ііі genes , and 2 strains (1.7%) were positive for blactx-m group іv. conclusion: the prevalence of extended-spectrum β-lactamases (esbls) are increasing significantly in hospitals of tehran. in other side, we found that the ctx-m і group had the most prevalence than other ctx-m groups.