A question about the bacteria in our bodies; I understand that our body had evolved to operate in symbiosis with millions (billions?) of bacteria within it, particularly in the gut.
So, if (I appreciate that’s a big ‘if’, but imagine some procedure was capable of it) every single bacterium in the interior and on the exterior of the human body was killed, would we be in big trouble?
How soon would we notice the loss? What would the symptoms be, and could we replenish the beneficial bacteria without kicking the bucket?
What would be the effects of a permanently sterile body?
Actually I understand that the realistic estimate is 100 trillion bacteria per human gut. About a kg of them per person spread out between some multiple hundreds of species.
Hmm. Eliminate them all …
Digestive issues first come to mind. You’d have to provide replacements for essential vitamins that we can only get by way of them, but Vitamin K, the B vitamins, etc. can be provided artificially. Most of our plant based nutrition would be wasted as without them we cannot digest plant cell walls. Without a very special diet and vitamins provided artificially though within a few weeks you’d possibly bleed to death as a result of Vitamin K deficiency or get scurvy from a lack of Vitamin C. If you didn’t dehydrate from the diarrhea that resulted from excess fluid being sucked into the stool from the undigested material first.
But assuming that there are other bacteria and various other buggers still in the world you’d probably die of an infection before that. The symbiotic bacteria keep those other ones out; even short course of antibiotics that only slightly alter the balance of power can allow for fungal overgrowth causing nasty vaginal yeast infections … I would guess it would be a matter of days before a nasty bug set up shop and went systemic without our symbiotic bugs in place.
Oh, nature’s experiment over how long to recolonize with healthy buggers - birth. Babies’ guts are sterile at birth and are colonized within a few days. Lots picked up through the passage through a healthy vaginal passage and some by way of the breast, but obviously even C-section kids who go directly into special care with nothing by mouth do to prematurity or illness manage it somehow adequately well most of the time. Now of course we are evolved to do it at that point; not sure if an adult could do so well.
And inspired by the question, it turns out that premature babies, over 1000g anyway, may benefit from having a supplemental source of beneficial bacteria to make up for their lack of the usual exposure and antibiotic exposure, with decreased risks of a severe illness caused by bad bacterial overgrowth in the gut (necrotizing enterocolitis - NEC) and overall mortality rate. I haven’t heard of probiotic use in the NICU as standard practice yet though. I may just be behind.
We still can’t do a good enough job with cellulose to digest it enough to absorb it but we do enough of a job to open up the cells to make the cell inards accessible.
Seems that the digestive issue would be a massive one (I’m assuming, judging by the link on probiotics, that there would be a number of other complications resulting from the lack of them), if we aren’t killed by an opportunistic infection first.
On babies, I was going to include this in the OP before I thought that such bacteria would reach the baby through the umbilical cord - am I incorrect in assuming this? How can the mother’s body filter out the bacteria - is the placenta able to eliminate 100% of bateria from reaching the baby?
The mother’s bloodstream shouldn’t be teeming with pathogens anyway - unless she’s gravely ill - and any that are floating around in there that haven’t yet been mopped up by her immune system would not make it across the placenta - because there’s no direct connection between the two bloodstreams (google ‘placental barrier’)
If you want to see the effects of no bacteria on a body, just take a heavy dose of antibiotics for a few days. You’ll see changes in bowel habits in a day or two – up to and including diarrhea.
When my mother was on chemotherapy, it destroyed the bacteria in her mouth that normally take care of the yeast Candida albicans. She got a yeast infection commonly called “thrush” throughout her mouth and throat.
It’s not that bacteria aren’t “allowed” into the bloodstream, so much as they aren’t allowed to remain there. Phrased differently, all of us, as a result of daily activities such as having a bowel movement or brushing our teeth, get bacteria in our blood. The vast majority of times, your immune system takes care of it and you’re not the worse for wear. However, if, say, your heart valves are scarred from a previous episode of rheumatic fever, the bacteria may lodge in the irregular surface of the scar (‘nooks and crannies’) and escape detection, or at least escape destruction. They can set up shop there and, ultimately, cause a very nasty infection of the heart valves called infective endocarditis.
In the case of infections going to the fetus, at least in animals, many of them could have an ascending infection that could affect the placenta (and fetus), but cause little or no damage to the mother. The mother, of course, is never septic. The bacteria gets access through the cervix somehow and infect upwards.
I’ve been wondering if someone could write a good end-of-the-world book based on what would happen if bacteria were to suddenly die off worldwide. *Dust *kind of approached the subject, but didn’t go far enough.
I don’t think we would be at all.
According to a story I read some time ago, and I can’t find it now, the vast majority of cells in our body are bacteria that aren’t part of our human makeup. That is they don’t contain human DNA. If we removed those, there wouldn’t be much left (relatively). I did find this (see symbioits)
It’s true that bacteria living in and on the human body outnumber the mammalian cells. But bacteria are so much smaller than mammalian cells that, if they disappeared, you wouldn’t really notice them physically gone except for the effects noted in the thread above.
Most bacteria live in the intestines. You excrete large quantities of them with every bowel movement. Others live in the pores of your skin and in various cavities such as the mouth, nose, sinuses, and ears. And in pretty much any other place you can think of: hair, under fingernails, in folds of your skin, etc. Your urinary tract is relatively bacteria-free (unless you have an infection in it) snce the bladder secretes certain substances which suppress the growth of microorganisms.
The bacteria on and in your body are generally beneficial in that they are not harmful where they are, but are better adapted to living in their particular spot than random bacteria from elsewhere. So they outcompete any foreign bacteria that happen to come along.
As far as fiction about them being absent or removed, John Varley’s Eight Worlds series has humans living off Earth in a bacteria (and other microorganism)-free environment. So doctors do not have to worry about maintaining sterile environments for surgery. This is easily the most fantastic and unbelievable part of this series. It’s impossible to remove all the bacteria from a human body without killing the human. But in that universe, they supposedly did that for all humans as well as animals, plants, ships, and various other stuff brought up from Earth. And never missed one.
