In part due to the Human Microbiome Project and related large scale efforts, there is increasing awareness that the microorganisms that live on and in us can modify risk for a number of chronic diseases including cancer. While Helicobacter pylori was the first bacterium to listed as a carcinogen, recent studies have begun to associate additional bacteria with cancers. Moving beyond association requires establishment of causality and biological mechanism. I will discuss these issues broadly and in the context of our recent efforts to query the role of the upper-GI microbiome in modifying risk for developing esophageal adenocarcinoma. Esophageal cancer is the fastest growing cancer in the US, rising nearly 600% from 1972 – 2002, suggesting a new environmental exposure. Esophageal adenocarcinoma is highly lethal with five year survival of less than 15%. Barrett's esophagus is a precursor to esophageal adenocarcinoma and H. pylori is a Proteobacterium colonizing the stomach of 50% of the world's population. Infection with H. pylori can cause peptic ulcers and gastric cancers but also shows a protective association for Barrett's esophagus and esophageal adenocarcinoma. Utilizing a large Seattle based prospective cohort of Barrett's esophagus participants, we investigated associations of H. pylori infection with development of cancer or genomic instability defined as tetraploid or aneuploid DNA content measured by flow cytometry and found a significant association of H. pylori infection with less aneuploidy. These results indicate H. pylori carriage has protective effects in the Seattle population and may act at the level of preventing genomic instability, an important step in cancer progression. Investigation of bacterial communities present in multiple niches within the upper GI tract of Seattle Barrett's Study participants (squamous esophagus, Barrett's esophagus, stomach body, stomach antrum) suggest relationships between these communities that may influence disease progression.

Citation Format: Nina R. Salama. The bacterial world and the genome. [abstract]. In: Proceedings of the AACR Special Conference on Post-GWAS Horizons in Molecular Epidemiology: Digging Deeper into the Environment; 2012 Nov 11-14; Hollywood, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(11 Suppl):Abstract nr IA17.