Corynebacterium (tagged purple) start at the base of the biofilm and grow all the way out. Other bacteria live within the Corynebacterium structure and streptococci (tagged green) live around the outside. The Findings It took about a decade to develop the idea, which became the CLASI-FISH imaging method.1 Dr. Mark Welch takes samples of dental plaque with a toothpick and fixes it, a process of preserving a biological specimen by terminating biochemical reactions so it doesn’t spoil, which kills the bacteria but preserves the spatial structure of the bacterial community. “We apply the fluorescent labels and then we do our fancy microscopy,” she says. bacteria transforms into nitrite. Our bodies can convert nitrite into nitric oxide, which dilates blood vessels and lowers blood pressure. “There have been studies that show that if you use anti-bacterial mouthwash during the time that your body is secreting the nitrate through your saliva, it can kill the bacteria that do this work that our bodies can’t do,” says Dr. Mark Welch. “They come back, of course, but it stymies the process.” When people eat leafy greens and absorb nitrate into the blood stream, the body concentrates the nitrate into saliva ten-fold so it can wash over the oral bacteria before returning to the alimentary canal. Oral microbiologists have known for the past 50 years that different bacteria live in different parts of the mouth. Oral microbiologists have known for the past 50 years that different bacteria live indifferent parts of the mouth. “We’ve known for a long time that if you want to find Strep salivarius , you have to look on the tongue,” says Dr. Mark Welch. Drs. Mark Welch and Borisy’s innovative imaging method revealed that dental plaque has highly organized, complex bacterial structures that they called “hedgehogs” because of the spiny appearance of the structures’ characteristic clusters of bacterial filaments.2 On samples scraped from the tongue, they discovered entirely different, but equally complex, bacterial communities that Dr. Mark Welch calls “bacterial high-rises, little microbial apartment buildings that these bacteria build on your tongue.”3 In the mouth, bacterial communities build enormous, complex structures and each bacterium is most influenced by the bacteria that are closest to it, one or two body lengths away, at most.4 Other bacteria will intercept any nutrients or other chemical from farther away. “Each bacterium is secreting all sorts of stuff into the saliva, and then in turn our bodies secrete stuff into saliva that influences how the bacteria behave,” says Dr. Mark Welch. “We secrete urea in our saliva, for example, which turns into ammonium, which raised the pH, which is good because it discourages the bacteria’s tendency to produce acid that eats away at enamel.” Our bodies also secrete nitrate, a chemical compound common in leafy greens and beets, into saliva, which oral 27 Issue 1 | 2024 | Issues and People
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