Antibiotics and Viruses
A made-up antibiotic aims at the part that builds a bacterium’s cell wall. Viruses have no cell wall, so there is nothing to aim at. A random simulation also shows what happens when a few hard-to-treat bacteria are mixed in.
The virus count does not change with or without the drug, because there is no cell wall to aim at. Medicines that work on viruses (antivirals) aim at other targets.
Ordinary bacteria (drug works): 1
Hard-to-treat bacteria: 1999
Virus: 400
Share of hard-to-treat among bacteria: 100%
Drug: active
Hard-to-treat bacteria were 1% at first and are 100% of the survivors after the drug. As ordinary bacteria fell, the few that remained grew.
Counts come from a random simplified model (the seed is fixed, so the same settings give the same result).
It is the bacteria that become resistant, not the human body. Here a few hard-to-treat bacteria are mixed in from the start, and once the drug thins out the rest, those left over multiply. How resistance really arises is more complicated.
How long the drug is used here is just a length chosen for this simplified model. It tells you nothing about how long a medicine should be taken.
How long to take a medicine depends on the illness and the medicine. Follow the instructions of the doctor or pharmacist who prescribed it and the package leaflet. Do not change the amount or the length on your own, and do not stop on your own just because you feel better.
Many illnesses, including most colds, are caused by viruses, and antibiotics do not work on them. How long to take an antibiotic depends on the illness and the medicine. Follow the instructions you were given.
How to play
Press Auto to replay how the bacteria and virus counts change over time. Compare with and without the drug, and change the share of hard-to-treat bacteria at the start. The slider below lets you go to any moment. Every name and number is made up.
Learn more
Antibacterial medicines work on infections caused by bacteria, and are said not to work on illnesses caused by viruses, such as colds and flu. Beta-lactams such as penicillin bind to an enzyme that acts in the last stage of building the bacterial cell wall and get in its way. A virus has no cell wall, so it has no such target. Antibiotics of other kinds aim at places besides the cell wall. Antimicrobial resistance (AMR) means bacteria and other germs stop responding to antibiotics; poor or unneeded use is named as one contributing factor. In 1928 Alexander Fleming noticed that a mould interfered with bacterial growth, and a team including Howard Florey and Ernst Chain later made it usable as a treatment.