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The effect of oral microbial composition on periodontal health and on systemic health has been, and is being established. The oral microbiome, in turn, can be altered by local and systemic diseases and conditions. Gastroesophageal reflux disease (GERD), has been associated with increased acidity in the oral cavity resulting in dental erosion, and controversially a reduced risk of periodontal disease. We hypothesized that presence of GERD was linked to a modified microbial profile in untreated GERD patients and that the use of proton pump inhibitor (PPI) drugs: potent disruptors of gut microbiome, in GERD patients might result in a salivary microbiome that is further distinct. Untreated GERD patients showed multiple differences in salivary microbiome as compared to healthy controls. Taxa found at lower levels related to the presence of GERD not treated by PPI included: Prevotella melaninogenica, Prevotella pallens, Leptotrichia, and Solobacterium moorei and thirteen others. In contrast, GERD patients chronically using PPI showed minimal differences in salivary taxa compared to healthy controls not using PPI.

Consumption of green tea (GT) extracts or purified catechins has shown the ability to prevent oral and other cancers and inhibit cancer progression in rodent models, but the evidence for this in humans is mixed. Working with humans, we sought to understand the source of variable responses to GT by examining its effects on oral epithelium. Lingual epithelial RNA and lingual and gingival microbiota were measured before and after 4 weeks of exposure in tobacco smokers, whom are at high risk of oral cancer. GT consumption had on average inconsistent effects on miRNA expression in the oral epithelium. Only analysis that examined paired miRNAs, showing changed and coordinated expression with GT exposure, provided evidence for a GT effect on miRNAs, identifying miRNAs co-expressed with two hubs, miR-181a-5p and 301a-3p. An examination of the microbiome on cancer prone lingual mucosa, in contrast, showed clear shifts in the relative abundance of Streptococcus and Staphylococcus, and other genera after GT exposure. These data support the idea that tea consumption can consistently change oral bacteria in humans, which may affect carcinogenesis, but argue that GT effects on oral epithelial miRNA expression in humans vary between individuals.