Characterization of Helicobacter pylori in Mongolia

Abstract

Background: Helicobacter pylori infection is strongly associated with gastritis, gastroduodenal ulcer disease and gastric carcinoma. The virulence of H. pylori strains increases with the presence of the pathogenicity island PAI, which encodes a Type 4 Secretion System and the oncoprotein CagA. Two major CagA types can be distinguished by differences in the repetitive EPIYA region in the C-terminal sequence; the more virulent East Asian CagA type with EPIYA-A, -B, and -D motifs and the Western CagA type with EPIYA-A, -B, and C motifs, the virulence of which is associated with the multitude of EPIYA-C motifs. Aim: To determine the predominant types and epidemiology of Helicobacter pylori strain EPIYA isolated from patients without gastric cancer living in 18 provinces of Mongolia. Materials and Methods: The biopsies taken during the gastroscopy of the study participants were dissected and cultured in a selective medium for the Helicobacter pylori culturing, and PCR analysis was performed to detect the CagA gene by extracting DNA from the culture according to the DNA isolation protocol. The PCR products were subjected to sequencing and the EPIYA motif of the CagA gene was identified. Results: In this study, the cagA gene was characterized in H. pylori strains isolated from Mongolians suffering from gastritis (80%) or ulcer (20%). The EPIYA region of 53 isolates was determined by PCR-amplification of overlapping cagA regions and subsequent Sanger sequencing. Only one H. pylori isolate carried the East Asian type (ABD) and 52 isolates the Western type of CagA, thereof 30 the EPIYA type ABC, 19 the ABCC type and one each of type ABCCCC, AAABC and AAAAB. An amino acid exchange from EPIYA-B to EPIYT-B was predominantly found in CagA proteins in strains with < 2 EPIYA-C copies (n=25/32; p=0.015) including the two EPIYA-A enriched CagA proteins, which have not been described to date. Due to the amino acid triplet preceding the EPIYA motif and strength of predicted phosphorylation, the multiple EPIYA-A motifs A2, A3 and A4 were shown to cluster with EPIYA-B and EPIYT-B with the unique feature of amino acid E in position − 4 to Y of EPIYA. Conclusion: Helicobacter pylori strains distributed in Mongolia are dominated by Western type CagA and the most common subtypes are ABC and ABCC. In our study, two EPIYA-A-rich subtypes AAABC and AAAAB were identified for the first time, and these subtypes are considered to be less virulence, but further in-vivo studies are necessary at the protein level.