Helicobacter pylori infects more than half of the world's population, making it the most widespread infection of bacteria. It has high genetic diversity and has been considered as one of the most variable bacterial species. In the present study, a PCR-based method was used to detect the presence and the relative frequency of homologous recombination between repeat sequences (>500 bp) in H. pylori 26695. All the recombinant structures have been confirmed by sequencing. The inversion generated between inverted repeats showed distinct features from the recombination for duplication or deletion between direct repeats. Meanwhile, we gave the mathematic reasoning of a general formula for the calculation of relative recombination frequency and indicated the conditions for its application. This formula could be extensively applied to detect the frequency of homologous recombination, site-specific recombination, and other types of predictable recombination. Our results should be helpful for better understanding the genome evolution and adaptation of bacteria.

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: Salmonella enterica is the etiological agent of salmonellosis, with a high infection rate worldwide. In Mexico, ST213 genotype of S. enterica ser. Typhimurium is displacing the ancestral ST19 genotype. Bacterial cytoskeleton protein complex MreBCD play an important role in S. enterica pathogenesis, but underlying mechanisms are unknown. In this study, 106 interactions among MreBCD and 15 proteins from S. Typhimurium Pathogenicity Islands 1 (SP-I) and 2 (SP-2) involved in both bacterial virulence and stress response were predicted in ST213 and ST19 genotypes, of which 12 interactions were confirmed in vitro. In addition, gene cluster analysis in 100 S. Typhimurium genomes was performed for these genes. The in silico and in vitro results showed a novel MreBCD interactome involved in the regulation of pathogenesis and stress response through interactions with virulence factors located at SPI-1 and SPI-2. Furthermore, both pseudogene presence and sequence variations in four tested proteins between genotypes resulted in differential interaction patterns that are involved in Salmonella motility and survival in eukaryotic cells, which could explain replacement of ST19 by ST213 in Mexico.