Microbiological aspects of antibiotic resistant Helicobacter pylori strains.

Resistance of Helicobacter pylori to antibiotics has been described for macrolides, nitroimidizoles, and fluoroquinolones. In 1996, the mechanism of resistance to macrolides was determined to be a point mutation on the 23S rRNA which leads to decreased binding of macrolides to the ribosome. Recently, mutations in the gene coding for nitroreductase have been linked to resistance to nitroimidazoles but more work will be necessary to determine whether this is the only mechanism involved. Point mutations have also been associated with resistance to fluoroquinolones. A decreased susceptibility to amoxicillin has been observed and may be linked to changes in the penicillin binding proteins. The same phenotypic methods generally used to test antibiotic susceptibility can be applied to Helicobacter pylori. The disk diffusion method can be used for macrolides, the E-test for amoxicillin, and the point limit method for nitroimidazoles but the reference method of all of these is the agar dilution method. Molecular methods such as polymerase chain reaction-RFLP and various techniques using hybridization can also be employed but to date they have only been used for macrolides. These techniques have the advantage that they can be applied directly to the biopsy specimen.