Zakaria Bameri - Dept. of Microbiology, Shahed University, Tehran, Iran
Mohsen Chitsaz - Dept. of Microbiology, Shahed University, Tehran, Iran
Parviz Owlia - Dept. of Microbiology, Shahed University, Tehran, Iran

Background and Objective: Organisms producing CTX-M β-lactamases are emerging as a source 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 β-lactamases producing strains and molecular assay for the identification ofCTX-M β-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 MICwhen 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 confirmatorytest. 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 positivefor 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.

Beta Lactamases, Klebsiella pneumoniae, Antibacterial Drug Resistance