Clarithromycin is a drug of choice to eradicate H.pylori and resistance to this drug is a predominant cause of treatment failure. In order to determine the prevalence of clarithromycin resistance in H.pylori isolated from Thai patients, drug susceptibility test was determined by the epsilometer test and agar dilution. Mutations in the 23S rRNA gene that are associated with macrolide resistance were analyzed by PCR and reverse dot blot hybridization. Gastric biopsy specimens from 150 patients were cultured for H.pylori isolation. Seventy-one (47.33%) gastric biopsy specimens yielded H.pylori-positive results. Of the 71 isolates determined by MIC testing, 31 (43.66%) were resistant and 40 (56.34%) were susceptible to clarithromycin. All of the 31 resistant isolates contained 23S rRNA gene mutations whereas 40 susceptible isolates contained wild-type sequences. Sequence analysis of the 425-bp PCR product (portion of the 23S rRNA gene) did not reveal mutation such as that described at position A2142G. On the contrary, our findings demonstrated a T to C transition at position 2182 for all resistant isolates. Two isolates contained double mutations at position T2182C and A2143G and 3 isolates contained double mutations at positions T2182C and A2223G. Reverse dot blot hybridization gave concordant results for mutation detection as those obtained from sequencing.
