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Change of point mutations in Helicobacter pylori rRNA associated with clarithromycin resistance in Italy.

Primary clarithromycin resistance is the main factor affecting the efficacy of Helicobacter pylori therapy. This study aimed: (i) to assess the concordance between phenotypic (culture) and genotypic (real-time PCR) tests in resistant strains; (ii) to search, in the case of disagreement between the methods, for point mutations other than those reported as the most frequent in Europe; and (iii) to compare the MICs associated with the single point mutations. In order to perform real-time PCR, we retrieved biopsies from patients in whom H. pylori infection was successful diagnosed by bacterial culture and clarithromycin resistance was assessed using the Etest. Only patients who had never been previously treated, and with H. pylori strains that were either resistant exclusively to clarithromycin or without any resistance, were included. Biopsies from 82 infected patients were analysed, including 42 strains that were clarithromycin resistant and 40 that were clarithromycin susceptible on culture. On genotypic analysis, at least one of the three most frequently reported point mutations (A2142C, A2142G and A2143G) was detected in only 23 cases (54.8%), with a concordance between the two methods of 0.67. Novel point mutations (A2115G, G2141A and A2144T) were detected in a further 14 out of 19 discordant cases, increasing the resistance detection rate of PCR to 88% (P<0.001; odds ratio 6.1, 95% confidence interval 2-18.6) and the concordance to 0.81. No significant differences in MIC values among different point mutations were observed. This study suggests that: (i) the prevalence of the usually reported point mutations may be decreasing, with a concomitant emergence of new mutations; (ii) PCR-based methods should search for at least six point mutations to achieve good accuracy in detecting clarithromycin resistance; and (iii) none of the tested point mutations is associated with significantly higher MIC values than the others.