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KMID : 0829320090120010030
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Korean Journal of Clinical Microbiology
2009 Volume.12 No. 1 p.30 ~ p.36
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Clarithromycin and Amoxicillin Susceptibility Testing of Helicobacter pylori by Disk Diffusion Method
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Sung Heung-Sup
Lee Jong-Wook
Lee Mi-Kyung
Kim Mi-Na
Kang Jung-Oak
Im Ji-Hoon
Lee Mi-Ae
Lee Hae-Kyung
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Abstract
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Background: CLSI provides a guideline only for a agar dilution method of testing clarithromycin susceptibility for Helicobacter pylori. This study was to evaluate a disk diffusion method for clarithromycin and amoxicillin.
Methods: One hundred and forty clinical isolates of H. pylori isolated from May 2005 to May 2007 were tested by the CLSI agar dilution method and a disk diffusion method using 2 μg (2CLR) and 15 μg (15CLR) clarithromycin disks and 2 μg (2AMX) and 10 μg (10AMX) amoxicillin disks. The interpretation criteria used for the disk diffusion method were established by linear regression and error rate-bounded method for disk diffusion zone of inhibition (DDZ) compared to MIC.
Results: Resistance and intermediate rates to clarithromycin were 21.4% and 1.4%, respectively. A number of isolates with MIC 0.5, 1, and 2 (μg/mL) to amoxicillin were 7, 2, and 1, respectively. For 2CLR and 15CLR, the coefficients of determination (R2) between MIC and DDZ were 0.931 and 0.923 (P＜0.001), respectively, and the criteria for resistance/susceptibility were 12/28 mm for 2CLR and 23/39 mm for 15CLR. For 2AMX and 10AMX, the R2 between MIC and DDZ were 0.478 and 0.421 (P＜0.001), respectively, and the criteria for resistance with breakpoint of 2 μg/mL were 21 mm for 2AMX and 32 mm for 10AMX. All isolates had DDZ＜60 mm with 2CLR and 2AMX, but 61.4% and 75.7% of the isolates had DDZ＜60 mm with 15CLR and 10AMX, respectively.
Conclusion: Excellent correlation and agreement between MIC and DDZ were found for clarithromycin and amoxicillin. With 2 μg disks, the susceptibility breakpoints were 28 mm or less; thus, two disks could be tested in one plate
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KEYWORD
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Helicobacter pylori, Agar dilution, Disk diffusion, Disk di-ffusion, Clarithromycin, Amoxicillin
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