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Metronidazole susceptibility testing for Helicobacter pylori: comparison of disk, broth, and agar dilution methods and their clinical relevance

By Arthur J. Decross, Barry J. Marshall, Richard W. Mccallum, Susie R. Hoffman, Leah J. Barrett and Richard L. Guerrant


Since the methods for metronidazole susceptibility testing of Helicobacter pylori have not been standardized or validated, we compared three methods that are used to test the metronidazole susceptibilities of 25 isolates of H. pyloni. Specifically, we examined the methods of Steer's replicator agar dilution, tube broth microdilu-tion, and modified Kirby-Bauer disk diffusion. The metronidazole disk zone sizes obtained by the disk diffusion method correlated w'ell (r = 0.74) with the MICs obtained by the agar dilution method. Afterward, the disk diffusion method was used to characterize the metronidazole susceptibilities of 44 isolates of H. pylori. Dual therapy (bismuth and metronidazole) proved to be highly effective against metronidazole-susceptible strains (81.6 % eradication rate) but fared poorly against resistant strains (16.7 % eradication rate; P < 0.01). Using agar dilution testing, we validated the modified Kirby-Bauer disk diffusion method for metronidazole susceptibility testing of H. pylori and conclude that it is practical, accurate, and clinically applicable. Metronidazole resistance among Helicobacter pylon strains is endemic in Third World countries, and about 15 to 35 % of the strains in Western countries are resistant as well (7, 18). The capacity to test metronidazole susceptibility prior to initiating therapy permits physicians to tailor ther

Year: 1993
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