Detection of CTX-M-β Lactamases in Isolated Klebsiella pneumoniae

Background and Objective: Organisms producing CTX-M β-lactamases are emerging as a source of resistance to oxyiminocephalosporins 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