Barrett's esophagus (BE) prevalence has increased steadily over the past several decades and continues to be the only known precursor of esophageal adenocarcinoma. The exact cause of BE is still unknown. Most evidence has linked BE to gastroesophageal reflux disease, which injures squamous esophageal mucosa and can result in the development of columnar epithelium with intestinal metaplasia. However, this relationship is inconsistent-not all patients with severe gastroesophageal reflux disease develop BE. There is increasing evidence that the host microbiome spanning the oral and esophageal environments differs in patients with and without BE. Several studies have documented the oral and esophageal microbiome's composition for BE with inconsistent findings. The scarcity and inconsistency of the literature and the dynamic phenomena of microbiota all warrant further studies to validate the findings and dissect the effects of oral microbiota, which are considered a viable proxy to represent esophageal microbiota by many researchers. This review aims to summarize the variability of the oral and esophageal microbiome in BE by using the example of Streptococcus to discuss the limitations of the current studies and suggest future directions. Further characterization of the sensitivity and specificity of the oral microbiome as a potential risk prediction or prevention marker of BE is critical, which will help develop noninvasive early detection methods for BE, esophageal adenocarcinoma, and other esophageal diseases.
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