NDLI: Influence of Variations in Test Methods on Susceptibility of Haemophilus influenzae to Ampicillin, Azithromycin, Clarithromycin, and Telithromycin

Content Provider	PubMed Central
Author	Fuchs, Peter C. Barry, Arthur L. Brown, Steven D.
Copyright Year	2001
Abstract	The National Committee for Clinical Laboratory Standards standard broth microdilution method for testing the susceptibility of Haemophilus influenzae to ampicillin, azithromycin, clarithromycin, and telithromycin was evaluated by altering one variable at a time. Variables that were tested included age of colony for inoculum preparation, inoculum density, test medium, incubation atmosphere, and incubation time. For the macrolide, azalide, and ketolide agents, incubation in 5 to 7% CO2 most significantly affected the MICs, producing nearly twofold increases for clarithromycin and telithromycin and a greater than threefold increase for azithromycin. For ampicillin, a 10-fold increase in inoculum density increased the geometric mean MICs for β-lactamase-negative strains from 1.50 to 2.45 μg/ml. In addition, 206 H. influenzae strains were tested for their susceptibilities to the same drugs by the broth microdilution tests in two media, as well as by agar dilution tests, disk diffusion tests, and Etests, on six different agar media. The three standard methods with Haemophilus test medium (HTM) compared favorably with each other except for a high minor discrepancy rate (27%) by the disk diffusion test with ampicillin and clarithromycin. Agar dilution test MICs on the five comparative media were generally higher than those on HTM agar but were only rarely more than one twofold concentration higher. Etest MICs of azithromycin and telithromycin were more than twofold higher than agar dilution and broth microdilution MICs on HTM; ampicillin Etest MICs were nearly twofold lower. The use of media other than HTM agar appears to have a minimal effect on susceptibility test results for the ketolide, azalide, or macrolide drugs that we tested against H. influenzae.
Related Links	http://dx.doi.org/10.1128/JCM.39.1.43-46.2001
Starting Page	43
File Format	PDF
ISSN	1098660X
e-ISSN	1098660X
Journal	Journal of Clinical Microbiology
Issue Number	1
Volume Number	39
Language	English
Publisher	American Society for Microbiology
Publisher Date	2001-01-01
Access Restriction	Open
Rights Holder	American Society for Microbiology
Subject Keyword	Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Microbiology (medical)

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