[Genotypic homogeneity and susceptibility to clarithromycin for clarithromycin-resistant Helicobacter pylori strains].

ABSTRACT

OBJECTIVE: To investigate the mixed infection of clarithromycin susceptibility and genotype of Helicobacter pylori resistant strains. METHODS: Ten single colonies were picked randomly from each of 16 resistant strains. Genomic DNA was prepared from single colony isolates and their parental clarithromycin-resistant strains by the hexadecyltrimethylammonium bromide (CTAB)-phenol extraction method. Susceptibilities of single colony isolates to clarithromycin were determined by agar dilution and mutations in clarithromycin-resistant isolates identified by polymerase chain reaction and restrictions analysis. Genotypes of 16 resistant strains and their single colony isolates were tested by the fingerprinting patterns of random amplified polymorphic DNA (RAPD). RESULTS: All single colony isolates derived from 16 resistant strains were also resistant to clarithromycin and had the A2143G point mutation in 23 S rRNA gene. The RAPD fingerprints of single colony isolates derived from the same patient were identical to each other and to the RAPD fingerprint of the corresponding parental isolate. CONCLUSION: Neither mixed susceptibility nor mixed genotype was found in clarithromycin resistant strains.