[Helicobacter pylori genotypes and their association with host's immune response]

The study of Helicobacter pylori phenotypes and genotypes is mainly focused on two groups of putative bacterial virulence factors: the cag pathogenicity island (PAI), for which CagA is a marker, and the vacuolating cytotoxin VacA. Several studies have shown the clinical relevance of the determination of IgG anti-CagA antibodies.

To assess the prevalence of vacA and cagA genotypes of H. pylori and the association with IgG anti-CagA antibodies in symptomatic patients.

We studied 50 patients (mean age 53 years, range 15-92). PCR amplification of the vacA s and m regions was performed using the primers described (J Biol Chem 1995; 270: 17771). For cagA PCR, primers described by Rugge et al. were used (Cancer 1999; 85: 2506) and determination of IgG anti-CagA antibodies was done according to the method described by Blaser and Perez (Cancer Res 1995; 55: 2111).

All 50 patients studied were positive for H. pylori. Of the 50 H. pylori strains, 7 (14%) were isolated from patients with peptic ulcer disease and 43 (86%) from patients with non-ulcer dyspepsia. The most frequent vacA genotype was s2/m2, associated with cagA-H. pylori strains (p < 0.01). Presence of cagA+ H. pylori strains correlated with the presence of IgG antibodies (Kappa = 0.680). Determination of IgG anti-CagA antibodies showed a sensitivity of 77.4%, specificity of 94.7%, positive value of 96% and negative predictive value of 72%.

The most frequent H. pylori genotype found in northeastern Mexico was vacA s2/m2, cagA-. The presence of this genotype correlated with the clinical presentations observed in these patients. In addition, CagA serology showed a great specificity and good sensitivity that allow us to use this assay to assess the prevalence of CagA+ strains in Mexico.