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Take a deep breath through your nose or mouth.

As air enters your nose, mouth, sinuses, throat, and even the esophagus—collectively known as the aerodigestive tract—it comes into contact with bacteria that live on the surfaces of these body sites.

Scientists at the Forsyth Institute have now identified and named the species of bacteria that live on the surfaces of the human aerodigestive tract. They added this data to the Expanded Human Oral Microbiome Database (eHOMD). This work was published recently in the journal mSystems.

The eHOMD is based on new analysis of publicly available microbiome data sets for different sites in the human aerodigestive tract. It builds on a project that Floyd E. Dewhirst, Senior Member of the Staff at Forsyth and co-author of the study, started in 1988. The database is a collaborative effort by researchers all over the world for understanding the bacteria of the mouth. Dr. Dewhirst created and maintains the database, which is housed at Forsyth and publicly accessible to anyone.

Knowing the species of bacteria, as opposed to only knowing their genus, is like being able to differentiate between a horse and a donkey. Having this level of detail gives scientists a much better understanding of the bacteria in our bodies. The eHOMD now opens the door for new microbiome research on the human aerodigestive and respiratory tracts.

“If you study the microbiome of the human nose, the sinuses, the mouth, the throat, the esophagus, or the lungs, this database is ideal for you to do any kind of microbiome study,” said Katherine P. Lemon, Associate Member of the Staff at the Forsyth Institute and senior author of the study.

The study also identified what species of bacteria are common in the healthy adult nostril microbiome. To achieve this, Isabel Fernandez Escapa, Director of the Sequencing & Bioinformatics Core at Forsyth and lead author of the study, used a new analysis technique to assign bacterial species names to DNA sequences from the nostril microbiome samples of 210 adults from the original Human Microbiome Project.

Dr. Lemon’s lab at Forsyth focuses on understanding how bacteria in the human nose interact with each other in order to identify beneficial nasal bacteria. Her team, which included Dr. Tsute Chen, Dr. Yanmei Huang and Mr. Prasad Gajare, found that just 19 species of bacteria account for 90 percent of all total bacteria in the nostril microbiome of 210 adults.

“Of those 19 species, one is uncultivated, meaning scientists have never been able to grow and study it in the lab,” Dr. Escapa said.

The eHOMD now serves as a tool for other scientists studying bacteria in the human aerodigestive and respiratory tracts. Dr. Escapa added, “In this study, we’re giving an example of how you can use the database, and we hope other scientists will now use it for their research.”