Diversity of VacA intermediate region among Helicobacter pylori strains from several regions of the world

Abstract

Helicobacter pylori is known to be a major cause of gastric carcinoma and peptic ulceration. cagA positivity and vacA's signal regions and mid-regions are well-characterized markers of H. pylori's virulence. Recently, an intermediate region has been identified as another strong marker of H. pylori-associated disease, and its i1 allele has been linked with severe diseases in colonized hosts. The goal of this study was to determine the prevalence of the intermediate alleles in H. pylori isolates from China, Turkey, and Uruguay and from U.S. Africans and to compare their distribution with other well-characterized virulence factors. Originally, 123 H. pylori strains were studied, but 3 were excluded due to the failure to amplify the intermediate region in these samples. Therefore, a total of 120 strains were analyzed: 30 Chinese isolates, 35 Turkish isolates, 30 Uruguayan isolates, and 25 U.S. African isolates. The s type and the m type were determined by PCR amplification. The i type was identified by PCR amplification and DNA sequencing. CagA status was determined by PCR methodology. There was a strong correlation among CagA positivity, s1, and i1 in Chinese, U.S. African, and Uruguayan isolates, but less correlation among these markers in Turkish isolates. A new intermediate variant (i3) was identified in 25.7% of Turkish strains and 3.3% of the Chinese strains. In summary, the distribution of CagA positivity and s1 correlated with the i1 in the three populations, except in the Turkish population, which showed a disproportionate representation of the i3 allele. Phylogenetic mapping confirmed the i-typing method previously defined and adopted for this study. The phylogenetic tree showed country-specific correlation with the intermediate region. Our results showed that the i1 allele is strongly associated with CagA positivity and the vacA s1 allele, suggesting its role as a virulence marker and potential predictor for clinical outcome.

FIG. 1.

Comparison of the amino acid sequences of an i1 and i2 strain of H. pylori. The sequences of strain 60190 and Tx30a were used to define i1 and i2, respectively. Regions defined as clusters A, B, and C are indicated. VacF1 and i1R refer to the forward and reverse primers used to amplify the intermediate region.

FIG. 2.

Phylogenetic tree based on the amino acid sequences of the vacA intermediate region of strains from China, Uruguay, Turkey, and U.S. Africans. i types are separated by color: i1, red; i2, green; and i3, blue. Strains are labeled by region or country of origin: E, East Asia; U, Uruguay; T, Turkey; and A, United States. Preceding the country of origin, some strains are labeled by the area of the stomach from which they were isolated: A, antrum; C, corpus. Key: E, East Asian; A, U.S. African; U, Uruguayan; T, Turkish; i1, red; i2, green; i3, blue.