Caviary to the general

I think it’s about time to speak up for the mouth; the bowels have been getting entirely too much attention lately -as if they’re the only successful owners of a microbiome, the only hall that can accommodate a massive rally without needing crowd control. And they seem to thrive on numbers more than quality; there are very few first-names in the bowels. Very few memorable leaders.

I have to say that I, who have never found a need to keep a cup of water by my bed for my teeth, have probably been spoiled. If my dotage had cursed me with an empty mouth, perhaps I would have been more inclined to oral thoughts, than laxatives, but you deal with what you have. I do not regret my teeth, but in barely noticing their presence when not holding a tube of toothpaste, my visits to their country have been somewhat mindless: twice daily visits and a bit of floss thrown in for exercise. I suppose the residents are appreciative, mind you, because they still stand at attention whenever they see me coming, and they seem to enjoy the visit without undue wobbling or whatever. And yet they do seem a bit worse for wear whenever I notice them in the mirror -certainly not long in the tooth like my grandmother used to say -admittedly not about her dentures though. But I digress.

The oral hygienists in my dentist’s office were always so busy scraping away with those little chisels near my gums that I’d never had a chance to ask many questions without risking  hemorrhage. Finally, though, one of them mentioned the concept of biofilms and plaques, as she whittled away at my enamel. And once, in a brave attempt to secure tenure, told me in a commanding voice how even regular brushing and flossing wouldn’t remove everything. It got me thinking about all the resident bacteria and slimy things that sort themselves out in my mouth without making a fuss about it. It was reassuring to me when she informed me that far from marauding bands of them terrorizing the gums and attacking the teeth, they’ve arranged themselves in little orderly groups -farms, I guess- in specific neighbourhoods. It all seemed so civilized.

And then I came across a fascinating article in the knowable magazine about the massive microbiological organization at work only millimetres from my lips. Along with some amazing microphotography of the residents, it was a Q&A with biologists Jessica Mark Welch, Gary Borisy, and dental researcher Floyd Dewhirst https://www.knowablemagazine.org/article/living-world/2019/oral-microbiome/

‘If you’ve ever brushed your teeth or swished some mouthwash, they’ve been in your sight: the hundreds of billions of microorganisms — mostly bacteria — that live in the average human mouth. Dangling from the hard palate, burrowed in the nooks and crannies of the tongue and intertwined in the plaque on teeth are the many hundreds of  species that make up the human oral microbiome… The Human Microbiome Project defines nine sites in the mouth — the tongue, palate, tonsils, sub- and supra-gingival plaque on teeth, the keratinized gingiva, the buccal mucosa, the throat, and saliva.’ Amazing what you can learn, eh? To me, it’s all just the mouth, though.

‘From the point of view of a bacterium, it matters what kind of surface you’re living on. The teeth are solid, they’re always there. If you can root yourself onto them, you’re not going to get dislodged unless someone pushes you off with a toothbrush or something. Bacteria such as Corynebacteria precipitate calcium from saliva… they turn into that calculus that your dentist scrapes off your teeth. They grow very slowly, but they thrive by gluing themselves to their surface… But if you’re on the cheek cells, which shed pretty frequently, you have to bind quickly and grow rapidly. The fundamental limit on the length of time you can be bound to your surface and remain in the mouth is likely to be one of the factors that really structure the bacterial community. Streptococcus do well on the cheeks. They’re the first to show up, they grow quickly and then they move on.’ Huh.

What I have always wondered about, though, is what about all those other things that get in there with food? Wouldn’t they have fights with the locals? Well, apparently not if the residents are walled off in their plaque forts. ‘Plaque is a biofilm — bacteria adhered to a surface, embedded in a matrix of their own making… Bacteria behave differently in a biofilm. There are parts of their metabolism they only turn on in a biofilm, and they tend to be more resistant to antibiotics and changes in the environment.’

‘The plaque is characterized by a shape of bacterial community we call a hedgehog, organized around Corynebacteria… [these] are the foundation of community, acting like the coral in the reef or the oak tree in the forest — creating the habitat that other organisms then inhabit at characteristic positions.’ For example, ‘around the outside of the structure are Streptococcus, and they stay in the aerobic zone, exposed to oxygen. They appear to be creating a low-oxygen zone in the interior that’s been occupied by different bacteria.’ But, wouldn’t you know it, ‘if you look at images of dental plaque and of a microbial community on the tongue, they’re just completely different… [when you look] at a microbial community scraped from the surface of the tongue, you see a gray core — dead human epithelial cells — with other bacteria forming these very dense communities growing outwards and expanding…’ I suppose you only hear about the suburbs though -everybody flees the dying city core nowadays. Of course, who’d want to live on a constantly wagging tongue?

Still, there are some friendly neighbourhoods. ‘We know that some bacteria in the mouth participate in our nitrate metabolism — how we take in nutrients from food, which can actually modulate blood pressure. If you consume a diet that is rich in nitrate, rich in green leafy vegetables, it will lower your blood pressure a little bit, but not if you use antiseptic mouthwash… that might be one reason why we, as the host, allow the bacteria to grow to such density. We have a reason to let them do that.’

The article goes on to describe some other advantages -and disadvantages- of the oral village, and yet, to my shame, I suspect I’ve tended to treat it more like Brigadoon -that Scottish village that appears for only one day every hundred years. It was feast or famine with the toothpaste when I was young, and since I moved a lot, only a warning lecture from the dental hygienist every few years would temporarily focus my attention on my mouth. I have to wonder why my teeth still talk to me.

But now, as age gradually wears my gums down, I’m beginning to understand: you’ve got to support your local biome -it’s family, and by and large, reliable. As long as you sweep the streets, and cut the front lawn, everybody gets along.

I still don’t trust the tongue, though -mine seems to go rogue a lot…

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