Antibiotics and antibiotic resistance
Antibiotics
- An antibiotic is a drug that kills bacteria or stops them growing.
- They have saved countless lives — but only against bacteria.
- And bacteria are fighting back, by becoming resistant.
How penicillin works
- Penicillin stops bacteria from building their cell walls.
- As the bacterium grows, its weak wall cannot hold it.
- So the cell takes in water and bursts.
Penicillin kills bacteria by:
Penicillin prevents cell-wall synthesis; the growing cell cannot hold the water it absorbs, so it bursts.
Why antibiotics don't beat viruses
- A virus has no cell wall and no chemical reactions of its own to attack.
- It simply uses the machinery of the host cell.
- So there is no antibiotic target in a virus — antibiotics do not work against viral illnesses like colds.
Why do antibiotics not work against viruses?
Antibiotics target bacterial structures/processes; a virus has none of these, using the host cell instead.
Antibiotic resistance
- A mutation can make a bacterium resistant — the antibiotic no longer kills it.
- By natural selection, the non-resistant bacteria die, the resistant ones survive and multiply, and resistance spreads.
Slowing resistance: only use antibiotics when needed; always finish the full course; use the correct antibiotic; reduce heavy use in farming.
Antibiotic resistance spreads because:
Resistant bacteria (from mutation) survive the antibiotic and reproduce, so resistance spreads by natural selection.
You've got it
- antibiotics kill bacteria — penicillin stops cell wall building, so the cell bursts
- they do not work on viruses (no cell wall, no target — uses host machinery)
- resistance: a mutation + natural selection → resistant bacteria spread
- slow it: only when needed, finish the course, correct drug, less farm use
Which action helps slow antibiotic resistance?
Finishing the course leaves no survivors; avoiding unnecessary use reduces the selection pressure for resistance.
Antibiotics should be taken to treat a common cold.
Colds are caused by viruses, which antibiotics cannot kill — using them needlessly only drives resistance.