FIG. 1.

Schematic of vacA midregions for the m1 and m2 allelic types, showing the original midregion allelic type-specific typing system (1) and the new PCR strategies. The diagram is drawn to scale except for the sizes of the arrows representing the PCR primers. The boxed area is 910 bp for strain 60190 (coordinates 1395 to 2304 numbered from the adenine of the start codon [8]) and 1,000 bp for strain Tx30a (coordinates 1371 to 2370 [1]). X represents an insertion of 75 bp, and Y represents an insertion of 15 bp; both are present in m2 alleles but not in m1 alleles. The arrows labeled VA3-F and VA3-R and those labeled VA4-F and VA4-R are the allelic type-specific primers used in our original PCR-based system (1). The solid lines labeled pCTB4 and VA6 are the allelic type-specific probes used for hybridization. VAG-F and VAG-R are the primers used in new strategy 1, and they anneal to regions of vacA conserved between m1 and m2 alleles; the types are then differentiated on the basis of PCR product size. Primers VA7-F and VA7-R and primers VA4-F and VA4-R are allelic type-specific primers used together in new strategy 2. Product size depends on which specific primers anneal, and the expected annealing primers are shown below the m1 and m2 regions.