Mutations in 23S rRNA in Helicobacter pylori conferring resistance to erythromycin do not always confer resistance to clarithromycin

Mutations conferring resistance to erythromycin or clarithromycin in Helicobacter pylori were studied. Mutation A2142G was consistently associated with clarithromycin MIC of > 256 micrograms/ml, whereas mutants carrying A2143G had MICs ranging from < or = 0.016 to > 256 micrograms/ml, suggesting that additional factors account for the observed multiple levels of resistance to clarithromycin.