Microbial communities in the esophagus and stomach are sparse and adapted to acidic environments.

“As you move down the digestive tract, there are microbes in esophagus in our stomach, but those communities are not very dense, and actually not very well studied. We know of a very... There's a very famous stomach bacteria known as Helicobacter pylori, which can cause stomach ulcers and cause gastric cancer in some less frequent situations. But this is a very different set of microbes, they have to be adapted to a different environment, in the stomach especially, incredibly acidic environment.”