Detection of CTX-M-β Lactamases in
Isolated Klebsiella pneumoniae
Volume
5
(2010) Issue
3 (Summer )
Original Article
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KeyWords:
Beta Lactamases, Klebsiella pneumoniae, Antibacterial Drug Resistance
Authors:
Zakaria Bameri, Mohsen Chitsaz, Parviz Owlia
Abstract:
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
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.
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