Which organism is most closely associated with gastric cancer?

• A. Campylobacter jejuni
• B. Helicobacter pylori
• C. Salmonella Typhimurium
• D. Yersinia enterocolitica

Answer: (B)

Long-standing infection with Helicobacter pylori is the strongest bacterial link to gastric cancer. This bacterium colonizes the stomach and causes chronic gastritis; over years, the ongoing inflammation can progress to atrophic gastritis, intestinal metaplasia, then dysplasia and finally gastric adenocarcinoma, especially the intestinal type. Virulence factors like CagA promote changes in gastric epithelial cells, and urease helps the bacteria survive the acidic environment, sustaining the inflammatory milieu that drives carcinogenesis. Importantly, eradicating H. pylori reduces cancer risk, which supports a causal connection. The other organisms listed are mainly associated with acute gastroenteritis or extra-gintestinal infections and do not have the same established link to gastric cancer.