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Comparison of screening methods for detection of extended-spectrum β-lactamases and their prevalence among Escherichia coli and Klebsiella species in Hong Kong

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Three tests, the disk diffusion test, the double-disc synergy test and the inhibitor-potentiated disc diffusion test, were compared for their abilities to detect production of extended-spectrum β-lactamases (ESBL) in 702 Escherichia coli and 472 Klebsiella spp. strains from four hospitals. Eleven percent E. coli and 13% Klebsiella spp. were found to produce ESBL. As an indicator of ESBL activity, the sensitivities of the five extended-spectrum β-lactams were as follows: cefotaxime (100%), cefpodoxime (99.3%), ceftriaxone (98.6%), aztreonam (93%) and ceftazidime (57.7%) when interpreted using the National Committee for Clinical Laboratory Standards criteria. Their positive predictive values ranged from 67.8–83.8%. Both the inhibitor-potentiated disc diffusion test and the double-disc synergy test (at three inter-disc widths of 20, 25 and 30 mm) were capable of identifying all the ESBL-producers. However, at a single inter-disc width of 30 mm, the double-disc synergy test has limited sensitivity (83.8%). As a second test for confirming ESBL activity in strains with reduced susceptibility to β-lactams, the inhibitor-potentiated disc diffusion test is therefore a simple and reliable option.

Keywords: Escherichia coli; Klebsiella species; extended-spectrum β-lactamases; screening methods

Document Type: Original Article


Affiliations: 1: Division of Infectious Diseases, Department of Microbiology, Queen Mary Hospital, University of Hong Kong 2: Departments of Pathology, Queen Elizabeth Hospital, 3: Tuen Mun Hospital and 4: Kwong Wah Hospital, Hong Kong SAR, China

Publication date: March 1, 2000

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