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> Matthew Olm (opens a new tab), a physiologist who studies the human microbiome at the University of Colorado, Boulder and was not involved with the study, is
by lolinder 2y ago
> Matthew Olm (opens a new tab), a physiologist who studies the human microbiome at the University of Colorado, Boulder and was not involved with the study, is “inherently skeptical” of the idea that populations of microbes could live in the brain, he said. But he found the new research convincing. “This is concrete evidence that brain microbiomes do exist in vertebrates,” he said. “And so the idea that humans have a brain microbiome is not outlandish.”
It's interesting to me that it would ever have been considered outlandish. In light of everything we now know about microbiomes and microbiology in general, it seems to me as a layman that the more radical proposition would be that the blood-brain barrier would be 100% effective at keeping out all bacteria, rather than the proposition that it probably isn't but that the bacteria it does let in tend to be symbiotic.
- dr_dshiv 2y agoSo, what does that say about the possibility of fungal symbiotes?
- outworlder 2y ago> it seems to me as a layman that the more radical proposition would be that the blood-brain barrier would be 100% effective at keeping out all bacteria, Bacteria is not usually found in most organs in the body though. Even more so in an organ as important as the brain that even our own immune system doesn't have access. The brain has its own cells to do that job. In order for bacteria to cross the blood brain barrier you need bacteria in the blood first, where they aren't normally found without getting under fire. Having bacteria in the gut is more obvious and makes more sense.
- eleveriven 2y agoBut bacteria are incredibly adaptable
- lolinder 2y agoThe lungs, mammary glands, uterus, ovaries, vagina, placenta, semen, eyes, skin, and nasal cavity all have their own documented microbiome so far, and we've been finding out about new microbiomes about once a year. They are not a thing that is reserved for the digestive tract.
- outworlder 2y agoThe brain is _unusually_ protected though. There's nothing like the blood brain barrier basically anywhere else. Most the the tissues you mentioned are exposed to the environment in some way. There aren't many ways to reach the brain without getting inside the body first(sensory organs being the obvious pathway, but even that is a stretch). Not saying it's impossible, just that the skepticism is warranted.
- forgotoldacc 2y ago> There's nothing like the blood brain barrier basically anywhere else. There is. The placenta and, oddly, prostate as well.
- __MatrixMan__ 2y agoIf you were to simplify the human body to a sphere (or torus... or whatever corresponds with the number of orifices that a human has), then all of the microbiomes you've listed would be on the exterior. The brain (and heart and kidneys and liver and bones and...) would not be. The microflora would need to have gotten there somehow, something analogous to endosymbiosis. But unless they're somehow getting from brain-to-egg-to-brain that's hard to explain. As for the others, they're easier, all being along the surfaces. Even the gut is on the "outside" in that membranes need not be crossed in order to access it. Although counterpoint: the same argument would apply to a fish so I guess it's not impossible. Just more surprising.
- Wilsoniumite 2y agoI think it depends a bit on how you count but I've heard it is an 8 holed donut
- __MatrixMan__ 2y agoIt also differs between individuals (e.g. one can develop a fistula).
- __MatrixMan__ 2y agoAgreed. Additionally, one of the mechanisms keeping the gut bacteria from taking over the rest of the body is an oxygen gradient: anaerobic bacteria in the gut are unlikely to be interested in an exploration of the aerobic environment of the body. Oxygen diffuses freely across the blood brain barrier, so it would not serve as an analogous containment mechanism.
- 20after4 2y ago> even our own immune system doesn't have access I thought that was recently found to be false? Or at least it isn't the full picture. see for example: https://www.science.org/doi/10.1126/science.abo7649 https://www.science.org/doi/10.1126/science.abo7649
- s1artibartfast 2y agoIt is certainly true as a rule of thumb, although there may be more going on locally that was previously thought
- panabee 2y agoThis is unrelated to your main point, more to clarify an edge case for those interested in learning more: B cells can breach the BBB under certain conditions. At least one pathogen, Epstein-Barr virus, is known to inhabit B cells.
- ghurtado 2y ago> Having bacteria in the gut is more obvious and makes more sense. It probably has to do with the fact that, topologically speaking, the stomach (and the whole GI tract) is technically on the outside of our bodies.
- kazinator 2y agoThe gut is an involution of the outside surface; whatever is in the gut is essentially outside of the body, the same way that the inside of the hole of a donut is actually outside of the donut.
- njtransit 2y agoIs it the blood brain barrier that keeps out bacteria or your immune system? Admittedly I know little about biology, but I thought bacteria growing inside your body was generally considered a “bad thing” (topologically speaking, your digestive system is outside your body).
- outworlder 2y agoIndeed. In order to even try to cross the blood brain barrier, an organism would have to be in the blood already. If that's unexpected, the immune system certainly won't like it. Large compounds and even immune cells aren't supposed to cross it. Usually brain infections are from tiny viruses because of that, unless they found another way (like ear, nose or eye infections, all of them effectively brain 'appendages'). Now, it could be the case that in a person with a compromised immune system AND a compromised blood brain barrier, that organisms would be able to live long enough to reach the brain. Once there, they would be mostly shielded from the immune system, except for brain glial cells (and I guess antibodies; usually the blood brain barrier stops most of them)
- haccount 2y ago[dead]
- dekhn 2y agoFrom what I understand about the BBB, it's practically impermeable to anything the size of a bacteria (mainly intended for gating small molecules like fats and drugs), until an individual has some sort of disease or other health problem that effects the BBB's integrity. But I can easily imagine that some bacteria (harmful, or helpful) could have exactly the right surface proteins to indicate it's permitted. I guess this review/writeup https://asm.org/articles/2020/april/how-pathogens-penetrate-the-blood-brain-barrier https://asm.org/articles/2020/april/how-pathogens-penetrate-... covers most of the known mechanisms for traveral of the BBB by pathogens.
- lymphbizkit 2y ago[dead]
- tomcam 2y agoI am skeptical that the brain wouldn't have a microbiome
- throwawaymaths 2y agoThere are regions of the body that almost certainly do not have a microbiome, for example the viteous humor
- tomcam 2y agoI’m talking about the brain in particular. A lot goes on and it consumes a ton of resources.
- F-Lexx 2y ago> A lot goes on and it consumes a ton of resources. But why should this be taken a sign of a brain microbiome? I fail to see the connection you're implying.
- tomcam 2y agoPure intuition, nothing more. I think we're just beginning to understand the microbiome and the brain does so much, has so many ports, and requires so many resources, that I think there are probably hundreds or thousands of heretofore unknown critters it relies on.
- seizethecheese 2y agoA start: do fish have a blood brain barrier that’s similar to humans?
- fasteo 2y agoThis is indeed the first question to ask. According to ChatGpt (don't beat me up) >>> Yes, fish brains have a blood-brain barrier (BBB)
- card_zero 2y agoYou can't just say "don't beat me up" and expect not to be beaten up. Anyway there's a pdf here that probably tells what kind of a BBB zebrafish have. https://www.mdpi.com/1422-0067/22/22/12111 https://www.mdpi.com/1422-0067/22/22/12111 And the article itself says "... communities of bacteria thriving in salmon and trout brains. Many of the microbial species have special adaptations that allow them to survive in brain tissue, as well as techniques to cross the protective blood-brain barrier."
- fasteo 2y agoha, I guess you are right https://en.wikipedia.org/wiki/Self-fulfilling_prophecy https://en.wikipedia.org/wiki/Self-fulfilling_prophecy
- glfharris 2y agoCSF sampling is a routine investigation in most hospitals. We don't typically see bacteria in these samples, when we do, its in the form of bacterial meningitis, hence the skepticism.
- biofunsf 2y agoWhen something seems obvious to me but scientists in the field disagree, I usually take this a sign I need to improve my own understanding.
- lolinder 2y agoUnfortunately as often as not this doesn't seem to be the case. Expertise in a field often seems to create blinders.
- eleveriven 2y agoAnd I think the brain, like other organs, might have its own microbial community, even if it’s a small or specialized one.
- sumitkumar 2y agoI like to think that the bacteria are only on the outermost layer of the body, i.e. skin. It just happens so that the respiratory and the digestive systems are the exterior part of the body which are inside our body. In other words epithelial cells mark the boundary of inside and outside and bacteria are usually tolerated on the outside and not inside.
- lm28469 2y ago> It's interesting to me that it would ever have been considered outlandish Not so long ago we thought fish or even human babies didn't feel pain, we take a lot of things for granted. https://hms.harvard.edu/news/long-life-early-pain https://hms.harvard.edu/news/long-life-early-pain