Helicobacter pylori virulence factors--one part of a big picture

At least half the world's population is infected with Helicobacter pylori, although only 10-20% of carriers develop gastric diseases, ranging from ulcer to MALT-lymphoma and adenocarcinoma (MALT is mucosa-associated lymphoid tissue). The clinical outcome of H pylori infection is determined by a complex interaction of environmental influences and host and microbial virulence factors. H pylori genotypes carrying the babA2 gene, encoding a bacterial adhesin mediating interaction with gastric epithelial cells, have enhanced pathogenicity. Moreover, coexistence of babA2 with other bacterial virulence factors further worsens clinical outcomes.

To further elucidate the clinical relevance of babA2-genopositive H pylori strains, Carlo-Frederico Zambon and colleagues analysed the association of babA2 genotypes with gastritis, gastroduodenal ulcer disease, or intestinal metaplasia in 167 infected Italian individuals. The coexistence of babA2 with other potentially disease-related H pylori genes, such as cagA, vacA, or oipA, correlated with clinical outcome. 36% of H pylori strains were babA2(-) genopositive, and abundance of babA2 was associated with the genomic presence of the other potential virulence-factor genes. H pylori strains carrying babA2, cagA, and the vacA genotype s1m1 were associated with the highest risk of developing intestinal metaplasia, whereas this condition was rarely (<10%) associated with strains with a cagA-, babA2-, vacA s2m2 genotype. Whilst the risk of developing more serious gastric lesions increased as the number of virulence factor genes accumulated in a given H pylori strain, there was no indication of any one specific bacterial gene-pattern being associated with a particular clinical disease. WHERE NEXT? Identifying the factors responsible for the enhanced pathogenicity of H pylori leading to development of life-threatening diseases in a subset of infected individuals is a mandatory task for the future. Identification of virulence-associated H pylori genes and investigation of their clinical relevance in large prospective studies will help to define such strains with increased pathogenicity. The value of H pylori genotypes as predictors of disease outcome is limited, because the pathogenic impact of bacterial virulence factors is greatly influenced by coexisting environmental and host factors.