Detection of CTX-M-(beta) Lactamases inIsolated Klebsiella pneumoniae

Background and objective: organisms producing ctx-m (beta)-lactamases are emerging as asource of resistance to oxyiminocephalosporins such as ceftriaxone and ceftazidime. however, thelaboratory detection of these strains is not well defined. in this study, phenotypic assay for screeningof extended-spectrum Ĉ-lactamases producing strains and molecular assay for the identification ofctx-m Ĉ-lactamases genes was developed and used to investigate the prevalence of these enzymesamong 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 dilutionmethod. a decrease of .3 doubling dilution in an mic for either ceftriaxone or ceftazidime testedin 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 fourprimer 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 confirmatorytest. using molecular assay, 117 strains potentially producing extended-spectrum-Ĉ-lactamases wereexamined for the presence of ctx-m enzymes. 88 strains (75.2%) were positive for blactx-m group .genes, 1 strain (0.85%) was positive for blactx-m group ... genes , and 2 strains (1.7%) were positivefor blactx-m group .v.conclusion: the prevalence of extended-spectrum Ĉ-lactamases (esbls) are increasingsignificantly in hospitals of tehran. in other side, we found that the ctx-m . group had the most prevalence than other ctx-m groups.