For decades, textbooks taught that peptic ulcers were caused mainly by stress or excess acid. In 1982, Australian pathologist Warren and young clinician Marshall repeatedly observed spiral bacteria in biopsies from chronic gastritis patients. They cultured the organism, named it Helicobacter pylori, and confirmed its pathogenicity in animal studies and Marshall’s famous self-infection experiment. H. pylori produces an enzyme called urease, generating ammonia that neutralizes acid and allows the microbe to survive. The resulting inflammation damages the mucosal lining and can develop into ulcers. When patients undergo antibiotic eradication therapy, ulcer relapse rates drop dramatically and quality of life improves. Persistent H. pylori infection was later linked to an increased risk of gastric cancer, making eradication a cornerstone of preventive medicine. Their work overturned dogma and showed that infectious agents can underlie chronic diseases, delivering enormous benefits to society.

Helicobacter pylori is a Gram-negative, microaerophilic spiral bacterium that swims through the gastric mucus using flagella and survives by urease-mediated acid neutralization. Between 1979 and 1983, Marshall and Warren examined gastric biopsy specimens with Giemsa stain and demonstrated a strong correlation between chronic active gastritis and H. pylori presence. In Marshall’s famous 1984 self-experiment, he ingested the culture, developed acute gastritis, and cured himself with antibiotics, providing near-complete fulfillment of Koch’s postulates. Subsequent work identified virulence factors such as CagA and VacA and delineated molecular pathways linking inflammation, epithelial damage, and carcinogenesis. Triple eradication therapy (PPI + amoxicillin + clarithromycin) became standard in the 1990s, reducing ulcer relapse rates to below 10 percent. Epidemiological studies estimate that over 75 percent of gastric cancers are attributable to H. pylori infection, leading WHO to classify the bacterium as a Group I carcinogen. These findings shifted the pathophysiological paradigm for peptic ulcer disease from an acid-centric model to an infectious disease model. Today, H. pylori research remains vibrant in the context of microbiome studies and antibiotic resistance, linking chronic inflammation to malignancy.

H. pylori exhibits high urease activity (~10^5 U), elevating local pH to 6–7 and, guided by chemotaxis, establishes a niche adjacent to gastric epithelial cells. CagA-positive strains inject CagA via a Type IV secretion system, leading to constitutive activation of SHP-2 phosphatase, cytoskeletal rearrangement, and enhanced IL-8 production. VacA forms anion channels and triggers mitochondria-dependent apoptosis, aggravating epithelial injury. Marshall’s early papers statistically correlated the morphologically defined HLOs with chronic gastritis scores under the Sydney system, an insight that challenged prevailing acid-centric dogma. Multicenter RCTs in the 1990s showed that ulcer relapse rates fell to odds ratios below 0.1 after eradication, prompting guideline revisions. Meta-analyses revealed that CagA-positive infection confers a relative risk of ~2.4 for gastric adenocarcinoma and an odds ratio >6 for MALT lymphoma. Rising clarithromycin resistance (23S rRNA A2143G) and metronidazole resistance (rdxA deletions) have spurred exploration of new regimens such as carbonyl-imidazole derivatives combined with vonoprazan. The prize underscores how cross-disciplinary research between gastroenterology and microbiology can dramatically improve clinical outcomes.