As you might well be aware of by now, our body is full of bacteria. All those little bugs that usually live there are together called the human microbiota. They are the reason why you are never truly alone 😉
Basically on all our surfaces, like the skin, in our nose, mouth, in our urogenital or gastrointestinal tract live bacteria. The skin and the mucosa in our nose and mouth are like a barrier for bacteria to keep them out of our body. This means that our internal organs are basically sterile, no bacterium there to be found… Or are they…?!
There are always those bad and nasty bacteria that are trying to cross this barrier. For this, they mostly take advantage of little injuries or cuts within the skin. When they reach deeper into our organs they cause infections or inflammation. And this is when you become truly aware that bacteria exist when they show you their nasty side…
This is supposed to be part of a series and here I want to start discussing how bacteria colonise our body (a.k.a. the host).
So, first of all, bacteria need to find the right host cell to infect and then they need to stick to it. For this, they are using a so called pilus. A pilus is a hair like structure that has a little patch at the end. The hair is like an extension that sticks out of the bacterium. When the patch at the end finds the right cell type, it sticks to it. So a specific bacterium can only stick to a specific cell type. For example, a bacterium that usually infects your bladder, can only stick to a bladder cell.
After a bacterium got stuck to a specific cell, it retracts its pilus, so it pulls itself closer to the cell.
On their surface, bacteria also have little hooks that are called adhesins. An adhesin binds specific protein components on the host cell. So after pulling itself close to the cell with a pilus, the adhesin or hook helps to tightly connect the bacterium with the host cell. And again, not every bacterium has the right adhesin to connect to every host cell type, they need specific ones for almost each cell type.
Once the bacterium is close to a cell, it fires off one of its many nano-weapons like the T3SS or the T6SS that were discussed in previous articles. With these, the bacterium makes the cell sick or makes it eat the bacterium so it can live inside… But how these mechanisms work, I want to discuss at a later point.
What does the host do?
So, obviously, our body doesn’t just let bacteria invade us. To avoid that bacteria come and attach to our cells, the body mainly uses shear stress. This means that there is a constant flow of either air or blood to wash off all bacteria from the cells, so they don’t get too attached. In our nose, we also have little hairs which move with every inhale and exhale. These moving hairs are also trying to wipe off incoming bacteria. Then there is also the mucosa itself, which is supposed to wash off bacteria from our mouth, nose or urogenital tracts.
And don’t forget our very own microbiota. The good bacteria on our body also help us fighting off incoming bad bacteria. And usually they are doing an amazing job, so be nice to them! And no more antibiotics to kill them!
And lastly, there is our good old immune system, which is what I usually like to call the bad side of microbiology. I will not focus much on this here, because you know… it is the bad side… But it is indeed important to help us fighting off incoming bacteria.
So, immune cells like for example macrophages swim around our body on the lookout for invading bacteria. There are more videos about this on Youtube, but I will just share this one here.
However, some bacteria found a way to just swim away from these immune cells by using their flagellum. (Remember the flagellum, that bacteria also use to find food?) Okay, so our little bacterium puts on some flippers to escape the immune cells, but that also means it has to find another host cell to attach to now. Which it will, eventually…
So, this was a bit of an overview of how bacteria colonise our body and what kind of obstacles it awaits in here. I hope I will manage to make this a series to tell you more about how bacteria then actually infect us as there is so much more to discover 🙂
So watch this space, subscribe to the blog (the button is at the bottom of this page) to stay informed about any new blog posts, or write comments and ask questions! 🙂