Differences in the Gastric Microbiotas of Neighboring Populations With Divergent Risks of Gastric Cancer

BACKGROUND: Although Helicobacter pylori plays a central role in gastric cancer (GC), other microorganisms involved in gastric dysbiosis may also impact carcinogenesis. We aimed to characterize gastric dysbiosis and its role in the transition from non-atrophic gastritis (NAG) to gastric premalignant lesions (GPLs) in two populations from Nariño, Colombia, with distinct GC risks: low-risk Afro-Colombians from Barbacoas and high-risk Amerindian-Mestizos from Cumbal. METHODS: Gastric biopsies from 200 individuals were analyzed using 16S rRNA gene sequencing. Microbial diversity and composition were assessed based on relevant clinical and sociodemographic characteristics. RESULTS: H. pylori infection was more prevalent in Barbacoas (83.8%) than Cumbal (70.5%), alongside higher rates of obesity (p < 0.001), alcohol intake (p : 0.07), and smoking (p : 0.02), but less severe OLGIM stages (p : 0.04). In Barbacoas, alpha diversity remained stable, whereas in Cumbal, richness significantly increased in GPL (p < 0.001). Beta diversity showed significant microbial composition differences between municipalities (p < 0.001). In Barbacoas, taxa such as Prevotella, Haemophilus, and Veillonella were dominant, whereas lactic acid bacteria such as Streptococcus were predominant in Cumbal. Barbacoas showed stable gastric microbiota composition across histological stages, whereas Cumbal exhibited enrichment of Gemella, Leptotrichia, and Prevotella in GPL. CONCLUSION: The Streptococcus-driven dysbiosis in Cumbal may help identify microbial biomarkers for GC progression, particularly other oral pathobionts.