In developing countries, clarithromycin resistance and frequency of re-infection are factors that contribute to high prevalence of Helicobacter pylori infection. The aim of this research was determine the prevalence of clarithromycin resistance and its relation with A2142G, A2142C and A2143G mutations in the domain V of the 23S rRNA gene of H. pylori isolates in patients from Southern Mexico with chronic gastritis. Another purpose of this work was to study the prevalence of virulent genotypes

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... d distribution of resistant strains according to the vacA/cagA/babA2 H. pylori genotypes. One hundred forty-four patients with chronic gastritis were studied. Forty-five H. pylori strains were isolated and clarithromycin susceptibility was determined by the diskdiffusion method. The 82.2% of the strains had the combination of alleles vacA s1m1 and the cagA gene was detected in 77.8% and 40% of the strains were babA2 positive. The vacA s1m1 genotype was detected more frequently in cagA + strains, vacA s1m1/cagA + /babA2genotype was more frequent than vacA s1m1/cagA + /babA2 + , 37.8% and 33.3%, respectively. Eight strains were clarithromycin resistant, in three of these, point mutations were identified, but only in one strain the A2143G mutation associated with clarithromycin resistance was found. that have not been associated with clarithromycin resistance were identified. The highest proportion of resistant strains was vacA s1m1/cagA + (62.5%). In patients from southern Mexico with chronic gastritis, the prevalence of clarithromycin resistance is within internationally accepted range (17.8%) and allows continued use of triple therapy for H. pylori eradication. However, it is necessary to monitor the evolution of clarithromycin resistance in this area. The largest proportion of resistant H. pylori strains is not harboring the A2142G, A2142C and A2143G mutations in the 23S rRNA gene (87.5%). The vacA s1m1/cagA + genotype was the most prevalent and among clarithromycin-resistant strains, this was the predominant.