what keeps us alive? Bacteria

Societies often have hierarchical structures. At the bottom of the pyramid you will find who actually does most of the work and as you move upwards you find entities that reap the benefits from the hard work of the lower class. Nature often works the same way, we just happened to be at the top of the pyramid, but we just ignore who is at the bottom.
I tried asking my friends for their opinion and the most common answer was: plants or herbivores, but I think that the very bottom there is another, very important, class that is often being overlooked, bacteria.
When we were kids we were thought to always wash our hands otherwise we would ingest bacteria (ignoring the fact that dirt always seems to find its way to kid's mouths anyway). So we were raised with this pre-concept that bacteria are bad and we should keep them away. Well, yes and no.

While it is true that some bacteria can kill us, it is also true that we would not be able to survive without them. In fact, if we were to count all cells in our body, to our surprise we would find that we actually host trillions of bacteria. In absolute numbers, we have at least 10 times more bacteria than human cells. Even inside our cells there are entities called mitochondria, that have bacterial origin but evolved in symbiosis with us and today they are the main "engine" that powers up our cells.

But where are all these bacteria?
Mostly in our guts, bacteria in fact help us break down foods and digest them. To better appreciate their importance, scientists tried to create germ-free rodents and study how they were doing. They found that rodents without bacteria in their guts needed to consume significantly more calories to maintain the same body weight and when later, they were given a dose of bacteria, the fat levels in their body spiked. Therefore, bacteria in our guts allow us to survive with less food. Without bacteria in our guts we would not be able to assimilate many nutrients from the food we eat.

But it's not just about guts, also in our mouths we have billions of bacteria. We need so many of them because they keep each other in check. In fact, a study found that people that have cavities often have fewer strains of bacteria in their mouth. A messed up diet with too many sugary foods can certainly disrupt the equilibrium in the microbiome that populates our body.

We often talk about "good" and "bad" bacteria, in reality this is not a black or white situation. We can sustain living with all these trillion of cells because we have balance, if we lose balance and a few strains of bacteria start being the predominant population in our body, we will most likely have problems.