EXPANDING ALLELIC DIVERSITY OF HELICOBACTER-PYLORI VACA

The diversity of the gene encoding the vacuolating cytotoxin (vacA) of Helicobacter pylori was analyzed in 98 isolates obtained from differe nt geographic locations. The studies focused on variation in the previ ously defined s and m regions of vacA, as determined bg PCR and direct sequencing. Phylogenetic analysis revealed the existence of four dist inct types of s-region alleles: aside from the previously described sl a, s1b, and s2 allelic types, a novel subtype, designated sie, was fou nd. Subtype sie was observed exclusively in isolates from East Asia an d appears to be the major sl allele in that part of the world. Three d ifferent allelic forms (m1, m2a, and m2b) were detected in the m regio n. On the basis of sequence alignments, universal PCR primers that all ow effective amplification of the s and m regions from H. pylori isola tes from all over the world were defined. Amplimers were subsequently analyzed by reverse hybridization onto a line probe assay (LiPA) that allows the simultaneous and highly specific hybridization of the diffe rent vacA s- and m-region alleles and tests for the presence of the cy totoxin-associated gene (cagA). This PCR-LiPA method permits rapid ana lysis of the vacA and cagA status of H. pylori strains for clinical an d epidemiological studies and will facilitate identification of any fu rther variations.