Bacteria on a petri dish in relation to our environment.

Question

How are the petri dish vs. your own body very different environments for bacteria? Like how is it that we can see the bacteria on a petri dish after touching it, yet we can't see the bacteria on our hands with the naked eye?

Answer 1

Bacteria are super tiny cells. We can't see them with the naked eye, so we don't see them on our hands, desks, doorknobs, etc.

However, when there's a bunch of bacteria in one place (like on a petri dish), there are SO MANY CELLS ( millions, billions) that we can see them as colonies or films.

Also, petri dishes are usually full of a solid media that contains all of the nutrients that bacteria need to grow and be very happy. You know how if you leave a piece of bread out for too long, it'll get moldy? That's because the fungus is really happy living on the bread and makes a lot of cells. The same concept can be applied to petri dishes and bacteria.