Question: Why do some antibiotics not work

David Walker-Sünderhauf answered on 8 Mar 2019: last edited 8 Mar 2019 11:00 am

When antibiotics are used, they kill bacteria. However, because bacteria aren’t stuck in time but are constantly evolving, by chance some of the bacteria can mutate and become resistant to the antibiotic you are using:
Using antibiotics puts this so-called “selective pressure” onto bacteria to become resistant. Now, this wouldn’t be a huge problem in itself – if you’re treating a bacterial infection that is resistant to one antibiotic you just use a different class of antibiotics to kill them! Unfortunately, it isn’t that easy: Often, the genes that make the bacteria resistant are located on bits of DNA that can be passed around between different bacteria, often even different bacterial species.

In this way, bacteria that make you ill can pick up one or several antibiotic resistance genes from other bacteria in the environment – that may have become resistant due to antibiotics use in farming, or from residues released from waste-water treatment plants. It is these superbugs, that have picked up multiple antibiotic resistance genes, that are causing the most problems in healthcare.

So overall, the antibiotics themselves don’t stop working – they may still work for some bacteria. The problem is infections by bacteria that have become resistant to these antibiotics!