H. pylori infection is a major risk factor for the development of invasive gastric adenocarcinoma, progressing through a multistep process involving active chronic inflammation, non-atrophic chronic gastritis, atrophic gastritis, intestinal metaplasia, and dysplasia [1]. Due to the high prevalence of H. pylori infection worldwide, its associated diseases pose a heavy disease burden for human health [17]. Accurate diagnosis and effective eradication of this pathogen not only improve the related gastrointestinal diseases but also reduce the risk of gastric cancer [7, 18]. The purpose of our work is to investigate the impact of H. pylori colonization density and depth on the severity of histological parameters of gastritis.

In the present study, nearly 90% of H. pylori-infected participants exhibited varying degrees of chronic active gastritis, with moderate activity (53.4%) being the most common. The similar result was found in the study of Souissi et al. [19] conducted in Tunisia.

Our study found significant associations between the density and depth of H. pylori colonization and the activity intensity of gastric mucosa inflammation since increasing the density and depth of H. pylori colonization increased the activity level of gastritis. Such a result was found in the study conducted in Iran [20] which revealed a significant dose–response association between H. pylori colonization density and the intensity of gastritis activity.

The findings of our study also showed significant correlations between the density and depth of H. pylori colonization and the severity of chronic gastritis in both overall and treatment-naive patients. While these correlations did not exist in people with a history of H. pylori eradication, possibly due to a longer duration of H. pylori infection. In previous studies conducted in Tunisia, Iran and Turkey, the relation between the intensity of H. pylori infection and the severity of chronic gastritis was all statistically significant [19,20,21]. However, this relationship was not observed in a study conducted by Park et al. [22] in Korea, nor in a study conducted by Choudhary et al. [23] in Nepal. This discrepancy may be owing to genetic variations, dietary habits, and environmental elements in different study populations.

Gastric atrophy and/or intestinal metaplasia was found in 35.8% of our subjects, which is lower than the percentage reported by Souissi et al. [19] (44.3% for atrophy and 10.3% for intestinal metaplasia) but higher than the percentage reported by Ghasemi et al. [20] (6.7% for atrophy and 12.5% for intestinal metaplasia). The different percentages of atrophy and metaplasia among these studies might be owing to differences in genetic backgrounds, age, dietary habits and the duration of gastritis. Furthermore, we found significant associations between the density and depth of H. pylori colonization and the severity of atrophy. The study results of Ghasemi et al. [20] confirmed the findings of our study. Surprisingly, we found that the likelihood of detecting atrophy decreased with increasing density and depth of H. pylori colonization, which could be attributed to the fact that the mucosal surface of atrophy and intestinal metaplasia was typically devoid of H. pylori colonization [15].

To some extent, H. pylori colonization density and depth were positively correlated with ulcer formation in this study. This finding is consistent with the study conducted by Alam et al. [24] in Michigan, which concluded a strong correlation between H. pylori colonization density and duodenal ulcer (P < 0.001), and a weak association between colonization density and gastric ulcers (P = 0.06).

No significant associations were found between the density and depth of H. pylori colonization and other histopathological findings, including lymphadenia, lymphoid follicle formation, glands cystic dilatation, intraepithelial neoplasia, dysplasia and eosinophil infiltration. A study conducted in Bangalore indicated that H. pylori colonization density was associated with the presence of lymphoid follicles and dysplasia [25]. This disparity might be due to the small number of patients with those histopathological changes in our study population.

Ultimately, we found a robust correlation between the colonization density and depth of H. pylori in patients with chronic gastritis, which has not been reported previously. Specifically, as the organism colonization density increases, so does the depth of colonization. When H. pylori colonizes gastric mucosa at a high density, the huge bacterial load will produce inoculum effect, which makes H. pylori adhere to gastric mucosal cells and form a protective biofilm. Biofilm-forming H. pylori is probably prone to survive for an extended period and evade the antimicrobial effects of antibiotics and immune responses of human body, consequently resulting in a persistent inflammatory reaction and tissue damage [26,27,28]. Studies have shown that CagA( −) bacteria primarily colonized the mucous gel or apical epithelial surface, whereas CagA( +) bacteria colonized the immediate vicinity of epithelial cells or intercellular epithelial spaces [29, 30]. It is reasonable to presume that the bacteria colonizing deeper layers are mainly CagA( +) strains with high pathogenicity. In addition, the bactericidal efficacy of antibiotics on deeply colonized H. pylori was diminished due to their inability to penetrate the thick mucus layer, causing persistent inflammatory responses. Therefore, assessing H. pylori colonization density and depth may serve as a valuable pre-treatment predictor of eradication therapy effectiveness. We recommend the utilization of more effective regimens, such as bismuth quadruple containing low-resistance antibiotics, to eradicate H. pylori in patients with severe bacterial colonization.

The main strengths of our study lie in its prospective design, large sample volume, and investigation of the impact of both H. pylori colonization density and depth on the severity of histological parameters of gastritis. Peer studies have mainly focused on the relationship between H. pylori colonization density and gastritis severity, but bare of articles have reported the association between H. pylori colonization depth and gastritis severity. If our present study was simultaneously conducted in multiple centers, it would possess a higher authority to draw conclusions from our current findings.