When I was a kid, my parents told me that everyday items are always filled with bacteria, such as banknotes, tabletops, keyboards, smartphones, floor (pick up your fallen food within 5 seconds or it will be infected with bacteria), I grew up told there are millions of bacteria under the fingernails all the time, is this really true? How can they be always there and survive that long if they are on the floor, banknotes etc.? They are living organisms, need to eat something, right? For my thinking there is nothing to eat on the banknotes normally. Can anyone bust this myth or confirm? Thanks in advance.
In: Biology
If you compared the total mass of humans and the total mass of bacteria alive today, there will be over 1000 times more bacterial mass than human.
If you assume that every surface (including liquids and even air) are *swimming* with bacteria you will almost never be wrong.
While my answer may touch some domains that are far-removed from ELI5, I hope it serves to spark inspiration and dispell concerns. I truly hope you, OP, go and learn more about this outside of Reddit. Because the microscopic world is just as incredibly beautiful and majestic as the heavens I frequently study!
One of my intellectual hobbies is something called “Artificial Life”. It’s the notion that with a few simple mathematical transforms at each time step, we can simulate the most basic behaviors of “life” instead of just the inert material it is composed of. Though there are a lot of different models (like Conway’s Game of Life, Emergent Gardens, and Lenia), there are a few conjectures that seem applicable to all of them. One of those being that *Life* **needs** *an environment filled with resources to flourish; once it reaches a “vacuum”, it eventually converges/terminates/halts/dies.* I know that seems round about, but this isn’t just the individual that dies. This means that ALL life ceases to flourish if there isn’t variability and resources available at every scale of existence.
So, why do I bring this up in this context? Let’s look at trees and corals. They are individually **MASSIVE** organisms, but they have tons of pockets with branches inside of them. They make the perfect home for smaller creatures like birds, fish, and invertibrates. But when you zoom in even closer, you find that some processes *need* other organisms who are specialized to process some raw materials into other things that are useful. Specifically with trees, they form a nearly symbiotic relationship with various mycilia (fungi): The fungi break down soil and other organic matter for the roots to absorb, and get excess sugars & water and a low-oxygen environment from the tree. But the thing is, mycilia are dumb; they just grow into whatever gaps they can find. And since they can be individual cells (though typically a culture), they can literally squeeze between two plant cells and make a nice home for itself without disrupting the tree. Just like how birds make nests! The key thing to note is that the fungi **is not** consuming the tree while the tree is still alive — That’d be like being a little kid eating the gingerbread house you live in!
In terms of magnitude, the difference in size between you and the sun is the same as between you and an organic molecule. And we’ve found living things so small that they even live inside of other cells! For example, I recently learned from [Kurzgesagt](https://youtu.be/GFLb5h2O2Ww?si=XjaGFyCcCD9Ap7v2) that TB bacteria are smaller than our macrophages (immune cells), take up residence inside of them, and replicate! As scary as that may sound, this is also a mechanism for evolution: Plant chloroplasts and all mitochondria were once bacteria that took up residence *inside* eucaryotic cells.
I like to think that all multi-cellular living things should be thought of like trees: Yes, lots of things live inside of us. But they are either doing no harm (like birds in trees, or the [little mites](https://youtu.be/YW2eGaUzq7E?si=pfvfSMzTFb6WJu4a) that live in our eyelashes) or doing something useful (like mycilia in roots, or [anaerobic bacteria](https://my.clevelandclinic.org/health/body/25201-gut-microbiome) in our colon). When things are out of balance, just like loss of habitat, that’s when the whole ecosystem (or in this case, your body) gets ill.
But you should take this message to all levels: ***We live on a giant wet bubble that can also be modeled as an unintelligent macro-organism! If we don’t start living benignly or beneficially in our environment, everything is going to wither & die.***
In an ELI5 way: Some bacteria hibernate in a variety of really impressive ways that can make them really resistant to a lot of threats. They can form a “shell” (ie become a spore). There are also specialized bacteria that eat basically every substance on earth, from each individual element to incredibly complex molecules like plastics.
Bacteria are also really good at forming symbiotic relationships which makes them even more adaptable.
The percent of bacteria that is harmful to any specific organism, like humans, is pretty low. So citrus canker (Xanthomonas citri subsp. citri) is really bad for citrus trees but doesn’t harm almost any other organism. Cholera mostly makes humans, rodents, and rabbits sick but isn’t going to sicken plants, insects, fungi, etc.
Not just the environment but in the body.
There are slightly more bacteria cells in your body than there are human cells
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4991899/
Your body right now has 30 trillion human cells in it, and 38 trillion bacterial cells. The human portion comprises more than 97% of your total weight. This illustrates how small bacteria are compared even to other living cells, and how you can have millions and not even detect them. As far as needing energy, they are not warm blooded, and do not need much energy to just sit around waiting for the next food source to become available, nor much of it.
It’s true, everything is colonized with bacteria. But our body is very good at fighting most of the popular ones.
Be careful of excessive cleaning though. Of course, cleaning things will kill the bacteria from a surface. But cleaning does something else as well: it resets the biotope for bacterias to colonize the surface again. This is a competition between the popular ones and the aggressive ones. Usually the popular ones win (they are the popular ones for a reason).
If you don’t clean again this is essentially harmless, as your body knows too damn well how to fight the popular ones.
But once in a while, the aggressive ones win the colonization race. Now if you don’t clean the surface again you get a full colony of aggressive bacteria, getting ill.
The solution is paradoxial: don’t clean so much so that the colonization race doesn’t start from scratch again. Give the popular bacteria a head start so they win the race. The one bacteria type your body doesn’t mind.
Did you ever hear about the science fiction scenario where someone invents nanobots and they take over the world in a [gray goo](https://en.wikipedia.org/wiki/Gray_goo) scenario, relentlessly turning everything they touch into more of themselves?
Well we live in the aftermath of that scenario. Hell, we *are* the aftermath of that scenario. Literally every niche that’s not lethal to dna-based life is full of dna-based life. Most of the biomass on the planet is bacteria. Heck, most of the cells in your body are bacteria. So, yeah, bacteria are everywhere.
IIRC a University did a study on the five second rule and reached two conclusions. 1) The rule doesn’t work. If the food lands in bacteria then it’s basically instant. 2) The University’s floors were clean enough to eat off of. [Found it: University of Illinois, 2003]
Yes, everything is “covered in bacteria”, but a lot of them are dead or dying, or in “suspended animation” hoping to get lucky and start growing again.
(Some are better able to survive long-term drying-out and exposure than others, and have different survival strategies, way too complex for ELI5 and frankly beyond my expertise. But overall, the fact they’re so simple compared to eukaryotic cells (cells with a nucleus, like most living things that aren’t bacteria) means they’re able to survive stuff that would kill cells of higher organisms or cause them to commit “suicide.”)
If something is coated in a large amount of bacteria, it’s going to be nasty/slimy (“biofilm” is the technical term), and a seriously bacteria-infected liquid is going to look very cloudy. But at that level, you’re probably talking about trillions of bacteria. (or more)
You know the film that forms on your teeth over the course of a day? Ever scratch at it with a fingernail and wonder what that off-white stuff is? Yeah…
A few million bacteria is nothing, because they’re tens of thousands or hundreds of thousands of times smaller (in terms of volume) than human and other higher animal cells. A bacterial “colony” the size of a largish grain of sand might contain over a billion cells.
So most of the ones coating everything don’t have the right conditions to grow (divide), which is why everything isn’t actually coated in a thin layer of disgusting slime all the time. 🙂
But because a bacterium typically needs less than one hour to divide if it has the nutrients, their numbers can increase exponentially very rapidly if they manage to find the right environment. (Although the human body is typically not a welcoming environment, because of our immune system and our own symbiotic “microbiome” which competes with any foreign interlopers.)
Anyway, so long, I just realized I need to brush my teeth…
Latest Answers