| Criteria | H. pylori Strain 26695 | H. pylori Strain P12 | Remarks |
| Origin | Isolated from a patient with gastritis in the UK | Isolated from a German patient with duodenal ulcer | Geographic and clinical origin influences genome and virulence profile |
| Genome Sequence Availability | First H. pylori strain to be fully sequenced (Tomb et al., 1997) | Fully sequenced; offers additional insights into strain-specific genes | Strain 26695 is the reference genome for many comparative genomic studies |
| Cag Pathogenicity Island (cagPAI) | Present and intact | Present and intact | Both strains are cagA-positive, capable of type IV secretion into host cells |
| CagA Protein | Expresses Western-type CagA with fewer EPIYA-C repeats | Expresses CagA with multiple EPIYA-C motifs | P12 CagA may be more potent in SHP2 binding due to higher EPIYA-C copy number |
| VacA Genotype | s1/m1 genotype, vacuolating toxin active | s1/m1 genotype | Both strains exhibit cytotoxic VacA activity |
| Type IV Secretion System (T4SS) | Functional; mediates CagA translocation | Functional; efficient in CagA and DNA transfer | P12 T4SS has also been used in studies on DNA delivery and transformation |
| Transformability | Moderately competent for natural transformation | Highly competent for transformation | P12 is widely used in genetic manipulation due to higher transformability |
| Laboratory Use | Reference strain for early genomic and transcriptomic studies | Preferred for infection models and mutagenesis studies | P12 is often used for infection assays, including polarized epithelial cell models |
| Colony Morphology | Small, transparent colonies on blood agar | Larger, more defined colonies | Differences may reflect variations in outer membrane or growth rate |
| Inflammatory Response Induction | Triggers moderate IL-8 secretion in gastric epithelial cells | Strong IL-8 induction and robust pro-inflammatory signaling | Suggests P12 may have higher immunostimulatory potential |
