Allelic variation in the vacA gene of Helicobacter pylori isolated from Chinese patients

OBJECTIVE: To characterize the vacA alleles present in Chinese Helicobacter pylori strains and to compare the allelic variation in the vacA gene of Chinese strains with that of Western strains. METHODS: Twenty-two single colonies of H. pylori isolated from five biopsy specimens with different gastric disorders were characterized for the expression of VacA protein and for evaluating the cytotoxic activity in HeLa cells. Five representative strains were selected and the vacA gene was amplified by PCR and subjected to automatic DNA sequencing using a primer walking strategy. RESULTS: Four strains expressed the VacA protein. Only one of the five strains induced vacuole degeneration in HeLa cells. All five vacA genes coded for identical signal peptides of the sla allele and had similar sequences encoding a 37 kDa subunit and outer membrane exporter. One of the five strains expressed a VacA protein with a middle region of the m1 allele and the others of the m2 allele. The four m2 allele strains had little vacuolating activity in HeLa cells. Phylogenetic analysis indicated that the homology of the Chinese vacA genes was 97.6–99.2% compared with 91.3–92.0% in the Western strains. CONCLUSIONS: There are allelic variations in the vacA gene between Chinese and Western H. pylori. Chinese H. pylori strains form a phylogenetically independent cluster separated from Western isolates. The m2-type strains seem to be more prevalent in China. Cytotoxicity in HeLa cells appear to associate with the middle region but not the signal sequence.