Annals of Clinical Microbiology, The official Journal of the Korean Society of Clinical Microbiology

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pISSN 2288-0585 eISSN 2288-6850

Comparison of Detection Methods of Extended-spectrum β-lactamase Producing Klebsiella pneumoniae and Escherichia coli

Original article

Annals of Clinical Microbiology (Ann Clin Microbiol) 2001 June Volume 4, Issue 1, pages 62-66.

Comparison of Detection Methods of Extended-spectrum β-lactamase Producing Klebsiella pneumoniae and Escherichia coli

Gyu Yel Hwang, Young Uh, Hyun-Joo Kim, In Ho Jang, and Kap Jun Yoon

Department of Clinical Pathology, Yonsei University Wonju College of Medicine, Wonju, Korea

Abstract

Background : Accurate detection of extended spectrum β-lactamase (ESBL) is important because ESBLs producing organisms may appear susceptible to oxyimino-β-lactams in standard susceptibility tests, but are considered to be clinically resistant to these drugs. Conventional antimicrobial susceptibility test methods do not reliably detect ESBL production. Molecular techniques and NCCLS broth dilution method, which detect ESBL production, may be time consuming, expensive and technically difficult to perform. The purpose of this study is to evaluate the clinical usefulness of NCCLS ESBL phenotypic confirmatory test by disk diffusion method.

Methods : For 96 Escherichia coli and 49 Klebsiella pneumoniae isolates collected between December 2000 to February 2001, double disk synergy test, NCCLS ESBL screening and phenotypic confirmatory test by disk diffusion test were performed. The ESBL producer was defined as organism showed an increase in the zone diameter of ≥5 mm for either antimicrobial agent such as cefotaxime and ceftazidime tested in combination with clavulanic acid versus its zone when tested alone.

Results : The sensitivity of NCCLS ESBL phenotypic confirmatory test were as follows: cefotaxime/clavulanic acid disk; 100% in K. pneumoniae and 83% in E. coli, and ceftazidime/clavulanic acid disk; 94% in K. pneumoniae and 67% in E. coli, respectively. Among the organisms with positive to NCCLS ESBL phenotypic confirmatory test, the detection rate of antimicrobial agents in double disk synergy test were as follows: K. pneumoniae; cefotaxime (84%), aztreonam (74%), and ceftazidime (52%), and E. coli; cefotaxime (44%), ceftazidime (44%), and aztreonam (39%).

Conclusions : The NCCLS ESBL phenotypic confirmatory test by disk diffusion method is easy, rapid, and sensitive method, suitable for routine use in the clinical laboratory. (Korean J Clin Microbiol 2001;4:62-66)

Keywords

Extended-spectrum β-lactamase, Klebsiella pneumoniae, Escherichia coli, Cefotaxime/clavulanic acid, ceftazidime/clavulanic acid