If you ask someone what the greatest invention of the 20th century was, oftentimes their answer will be antibiotics. We’ve all heard of them, perhaps we’ve needed to take them to treat an illness or infection. But what is an antibiotic? And how does it even work?

To start with, an antibiotic is any kind of substance that targets bacteria. Now, “targets” can mean many things; some antibiotics kill bacteria, others slow them down their replication, and others can hold them back from making proteins. Many kinds of antibiotics are developed in labs, but others can actually be found in nature. For example, Penicillin, one of the most famous examples of antibiotics, actually comes from a type of mold (or mushroom)!

But how do they work? How do these drugs figure out what to target when we take them? Well, the main way has to do with the structure of our cells in relation to bacterial cells. Human cells are eukaryotic animal cells, while all bacteria are prokaryotic cells. A main feature of bacterial cells is that they have cell walls made of a protein called peptidoglycan. Our cells don’t have cell walls though! This is what makes it so easy to differentiate our regular cells from bacteria, and why antibiotics work so well. Going back to the example of penicillin; when it enters the body, it immediately works to block the building of cell walls in newly formed bacterial cells. Without a cell wall to protect them from the outside environment, substances from the human body can freely enter bacterial cells and poison them.

There are a few issues with antibiotics, though. First of all, we need bacteria to survive. There are millions of bacteria living in our digestive system that help us metabolize our food and absorb important nutrients. Unfortunately, antibiotics aren’t able to differentiate between our “good” bacteria and the “bad” bacteria from outside, so there are a few nasty side effects that come with taking them. This isn’t the end of the world though, what’s much worse is the resistance certain bacteria are developing towards antibiotics. The more we take these drugs, the more bacteria can adapt and eventually build up immunity to them. Bacteria are living creatures after all, they can learn how to protect themselves just like we can. New antibiotics are constantly being developed in a race between people and bacteria, and so far we haven’t been able to figure out a surefire way to shut down bacterial infections for good.

Overall, antibiotics were certainly a brilliant discovery and have saved countless lives. However, it’s important to be cautious about overusing them. They’re powerful for sure, but so are bacteria!