We determined the MICs of amoxicillin, clarithromycin, azithromycin and ciprofloxacin for 21
Helicobacter pylori strains by using Mueller Hinton semi-solid agar without CO
2 incubation. Generally, the susceptibility of
H. pylori to these antimicrobial agents was measured by the agar dilution method with incubation in 10-15% CO
2 at 37°C. However, the MICs of macrolides in medium at pH 6.0 in CO
2 were 8-16 times higher than those at pH 7.0.
H. pylori strains of 1.0×10
7 CFU were inoculated into 1-ml of quantities semi-solid agar (prepared with Mueller Hinton broth to which 2 g of agar per liter was added) in tubes. The tubes were aerobically incubated at 35°C. The tubes were examined for growth of
H. pylori at a depth of 3 mm from the surface of the medium. Variation in the inoculum size did not affect the MICs of the four drugs. MICs of the antimicrobial agents except for ciprofloxacin used for quality control strains of the National Committee for Clinical Laboratory Standerds were within acceptable ranges. The MICs of the four drugs (except the twofold dilution of ciprofloxacin) which were measured for 3 days were within the acceptable range. The use of semi-solid agar for the measurement of MICs will assist clinicians in providing appropriate therapy for infections with
H. pylori.
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