**2. Genotyping of** *H. pylori* **strains**

After strains J99 and 26695 were sequenced, the first DNA microarray could be designed [13], allowing the first genotyping studies of diverse strains of *H. pylori* to be conducted*.* The first study compared 15 *H. pylori* isolates and observed that 362 genes (22%) were variable among the strains, which were called strain-specific genes. Subsequently, another study explored the genomic diversity of *H. pylori* isolates from children and adults who presented a single or a mixed infection (the presence of more than one strain). The number of variable genes in individuals with a mixed infection was found to be higher than that in individuals infected with a single strain. No difference was observed in the number of strain-specific genes between strains from children and adults [14]. However, a study of 56 strains from different geographical regions observed that 25% of the genomic content between these strains corresponded to strain-specific genes [6]. The genetic content of the strains has also been correlated with their pathogenesis in an animal model [4, 15]. Moreover, Romo-González et al. [16] identified and compared the differences in the genetic content of strains isolated from Mexican patients with non-atrophic gastritis, duodenal ulcers and gastric cancer. The authors observed that the core genome shared by these isolates was composed of 1319 genes, while 341 genes (20.5%) were strain-specific among the assayed isolates, 37% of which were distributed within the PZs. The genotyping analysis provided an understanding of which genes are present and absent in the isolates associated with each disease, making it possible to associate some of these genes with specific diseases.
