Free recombination within Helicobacter pylori

Abstract

Sequences of three gene fragments (flaA, flaB, and vacA) from Helicobacter pylori strains isolated from patients in Germany, Canada, and South Africa were analyzed for diversity and for linkage equilibrium by using the Homoplasy Test and compatibility matrices. Horizontal genetic exchange in H. pylori is so frequent that different loci and polymorphisms within each locus are all at linkage equilibrium. These results indicate that H. pylori is panmictic. Comparisons with sequences from Escherichia coli, Neisseria meningitidis, and Drosophila melanogaster showed that recombination in H. pylori was much more frequent than in other species. In contrast, when multiple family members infected with H. pylori were investigated, some strains were indistinguishable at all three loci. Thus, H. pylori is clonal over short time periods after natural transmission.

Figure 1

Representative compatibility matrices of alleles from different species. White spaces represent pairs of informative sites that are compatible with a maximal parsimony tree and black spaces show pairs of sites that could not be accommodated by such a tree. The genes selected from each species were broadly representative of the other genes examined and were chosen as including approximately the same number of informative sites. Quantitative mean neighborhood similarities are given in Table 2.