This podcast episode features Dr. Jessica Mark Welch of the ADA Forsyth Institute, who discusses the complex spatial organization and interactions within the oral microbiome. Dr. Mark Welch explains her lab's use of advanced fluorescence in situ hybridization (FISH) coupled with hyperspectral microscopy, a powerful technique that allows for the multi-color visualization of different bacterial taxa in their native environment without needing to culture them. This "microbiogeography" approach reveals that the mouth contains distinct, highly structured ecosystems. On the tongue, bacteria form "high-rises" on filiform papillae, while dental plaque consists of "hedgehog structures" where foundational species like Corynebacterium create a physical scaffold for other microbes to colonize in specific layers based on oxygen tolerance and other factors. The conversation explores the systemic health implications of these communities, particularly their role in converting dietary nitrate to regulate blood pressure, which raises questions about the indiscriminate use of antiseptic mouthwashes. The highly structured oral environment is contrasted with the gut microbiome, described as a "partially mixed bioreactor" where the host actively prevents stable biofilm formation.
Unveiling the Microbial Ecosystems in Your Mouth
7:35 Advanced Imaging of Microbes: Dr. Welch details her lab's key technique: fluorescence in situ hybridization (FISH). They use fluorescent DNA probes targeting ribosomal RNA to simultaneously label up to 10 different types of bacteria with different colors, revealing their exact spatial relationships ("microbiogeography") in a sample.
13:10 Distinct Oral Niches: The microbial communities on the tongue are almost entirely different from those on the teeth. Different surfaces in the mouth act as unique habitats, selecting for specific bacteria that can adhere to them, even though saliva constantly moves microbes around.
18:43 Your Microbiome is a Unique Fingerprint: While the bacterial species found on people's tongues are generally the same, the specific strains are unique to each individual. Studies show that people in close contact, like couples, share a significant number of strains.
25:15 The Link Between Oral Bacteria and Blood Pressure: A critical connection to overall health is the role of oral bacteria in converting dietary nitrates (found in beets and leafy greens) into nitrite. The body then uses this to produce nitric oxide, a vasodilator that helps lower blood pressure. Using an antiseptic mouthwash can disrupt this beneficial process.
29:52 The Architecture of Dental Plaque: Dental plaque is not a random collection of microbes but a highly organized structure. Dr. Welch describes "hedgehog structures" where Corynebacterium acts as a foundational scaffold, like an "oak tree." This allows other bacteria to colonize in layers, with oxygen-tolerant microbes on the surface and anaerobes in the protected interior.
39:00 Complex Microbial Interactions: At the tips of these structures are complex communities called "corn cobs." The interactions here are not simple; they involve both competition (some streptococci produce hydrogen peroxide as a form of "chemical warfare") and co-dependency (microbes rely on their neighbors for essential nutrients they cannot make themselves).
44:33 The Mouth vs. The Gut: The highly structured oral microbiome is contrasted with the gut, which Dr. Welch describes as a "partially mixed bioreactor." In the gut, the host actively prevents the formation of stable biofilms through mucus secretion, rapid shedding of cells, and physical mixing, keeping the microbes in a more planktonic (free-floating) state.
1:04:28 Takeaway Advice for Oral Health: Dr. Welch recommends physical removal of microbes through brushing, flossing, and tongue scraping. However, she suggests that routine "chemical warfare" with strong antiseptic mouthwashes may be counterproductive, as it disrupts a co-evolved and often beneficial microbial community.