We have already discussed the idea that some bacteria have always been resistant to certain antibiotics and that each antibiotic only has an effect on specific germs (See the antimicrobials section). But sometimes bacteria can become resistant to antibiotics that previously killed or damaged them. This resistance can develop in the following ways:
- A random change in the genetic material of the bacteria, this is known as a mutation. This can cause the genetic material to make the bacteria resistant to harm by the drug.
- By 'picking up' genetic material that contains instructions that code for antibiotic resistance. This genetic material can come from viruses, other bacterial cells or plasmids, which are loops of DNA in a bacterial cell that are separate from its chromosome (bacteria only have one single chromosome, unlike us humans who have 23 pairs in each cell). These plasmids can move from bacteria to bacteria, picking up and depositing bits of genetic material as they go. If the plasmid contains a bit of genetic material that codes for antibiotic resistance this can be spread to many other bacteria.
So this explains how antibiotic resistance can develop but it doesn't explain what effect these genetic instructions have on stopping the antibiotic from harming the bacteria. They can do this in a number of ways:
- Inactivating the antibiotic before it reaches the bacterial cell
- Reducing the uptake of the antibiotic into the bacterial cell
- Increasing the amount of antibiotic that is pumped out of the bacterial cell
- Altering the antibiotic's target on the bacterial cell so that the antibiotic cannot recognise and target the cell
- Activating different ways of multiplying, feeding, maintaining its structure etc, so that it can function despite the effect of the antibiotic (See the antimicrobials section for an overview of how antibiotics can interfere with a bacteria's life processes)