Question: How do u find bacteria?

Ciarán O'Brien answered on 11 Nov 2014:

There are several different ways we can find bacteria.

One way is culturing them: You make a little dish filled with loads of chemicals that most bacteria like to eat, and spread a sample on it to see if anything grows. That’s a bit messy as all the bacteria will grow together and it’s very hard to tell them apart. A better way of doing this is to make a load of dishes, each with different combinations of chemicals that some bacteria will eat and some won’t, and if those bacteria are in your sample, they’ll only show up on the foods they’re able to grow in.

This is how microbiologists have been finding bacteria for hundreds of years. But it has its problems. Some bacteria are really picky eaters, or they won’t grow if there’s any oxygen in the air, or they need to grow at a very specific temperature, or they need other bacteria present to help them grow, which makes things very messy. About half the bacteria that live in your gut just won’t grow for us if we use this method.

in the last couple of decades we’ve started finding bacteria by looking at their DNA. Not just one species at a time, either. All of them, at once! Every species of bacteria has unique DNA, and we can use it like a fingerprint or ID card to find what’s there. If we find DNA that doesn’t match up with all the DNA we’ve identified before, then it must belong to bacteria we haven’t seen before.

This is much better for finding bacteria than the old way, as we can find way more, and we don’t have to spend time figuring out what they like to eat and grow on, and it’s much quicker. We call it “metagenomics”. It’s the main way I use to find bacteria. There are thousands of different species of them in your gut and even if we could grow them all, it’d take forever to get through them all.

That said, the old ways are still useful for a whole load of reasons, like seeing if an antibiotic is good at killing bacteria (if you put a little piece of an antibiotic on the dish, bacteria won’t grow near it if it’s able to kill them).