Section 1 of 7Cause or symptom?
| Medicine type | What it does | Example | Works on viruses? |
|---|---|---|---|
| Antibiotic | Kills bacteria or stops them growing, so it treats the cause of a bacterial infection | Penicillin | No |
| Painkiller | Reduces pain or inflammation but leaves the pathogen alone, so it treats only a symptom | Ibuprofen, paracetamol | Only relieves symptoms |
| Antiviral | Interferes with the way a particular virus reproduces inside body cells | Aciclovir | Only the virus it was designed for |
| Antihistamine | Blocks the chemical released in an allergic reaction, easing symptoms such as itching and sneezing | Loratadine | Not relevant |
Section 2 of 7Using antibiotics
Matched to the infection
- Matched to the infection Different bacteria are killed by different antibiotics,
- so doctors choose one known to work against the one causing the illness.
- A sample of the infected tissue may be tested in the laboratory to find out which antibiotic works best.
Harm only bacteria
- Harm only bacteria Antibiotics disrupt processes found in bacteria, such as building a cell wall, so human cells are not damaged.
- Human cells have no cell wall, which is why they are unaffected.
Not for viruses
- Not for viruses Viruses live and reproduce inside body cells, so a drug that attacked them would risk damaging the body's own cells.
- This is why antibiotics do nothing for colds and flu, which are caused by viruses.
Big benefit
- Big benefit Since the 1930s antibiotics have saved millions of lives and cut deaths from infection.
- Operations such as organ transplants depend on antibiotics to prevent infection afterwards.
Section 3 of 7How resistance arises
1Random mutation
- Random mutation A bacterium in a population mutates and is no longer killed by an antibiotic.
- This happens by chance, not because the antibiotic was used.
2Antibiotic used
- Antibiotic used Non-resistant bacteria die but the resistant one survives, because it now has an advantage.
3Survivor reproduces
- Survivor reproduces It divides quickly, sometimes every 20 minutes, and passes on its resistance to every new cell.
4Resistant strain spreads
- Resistant strain spreads The antibiotic no longer works on the disease, a form of natural selection.
- Resistant bacteria can then be passed between people.
Section 4 of 7Slowing resistance
1
Doctors should not prescribe antibiotics for viral infections or very mild illness, because every unnecessary use gives resistant bacteria a chance to be selected.
2
Patients must finish the whole course so that all the bacteria are killed, not just the weakest ones, otherwise tougher survivors can multiply.
3
Use narrow-spectrum antibiotics where possible and keep the strongest ones in reserve for infections that nothing else will treat.
4
Restrict the routine use of antibiotics in farming so that fewer resistant bacteria develop in animals.
5
Develop new antibiotics, because resistant strains such as MRSA already exist and the number of effective drugs is shrinking.
Section 5 of 7Worked example: a resistant infection
Patient with an MRSA wound infection
What is happening
- What is happening The bacteria in the wound carry a mutation that makes them resistant to methicillin and several other antibiotics.
Why the usual drug fails
- Why the usual drug fails Standard antibiotics kill the non-resistant bacteria only, leaving the resistant ones to reproduce.
What doctors do
- What doctors do They test which antibiotics still work and may use a reserve drug, while isolating the patient to stop the strain spreading.
Lesson for the future
- Lesson for the future Careful prescribing, hand-washing and new drug research are all needed to keep infections treatable.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Antibiotic | A medicine that kills bacteria or prevents them from growing. |
| Painkiller | A drug that relieves pain without curing the disease. |
| Resistance | When bacteria are no longer killed by an antibiotic. |
| Symptom | A sign of a disease that the patient notices, such as pain. |
| Natural selection | The survival and reproduction of organisms with helpful inherited features. |
| MRSA | A strain of bacteria that is resistant to many common antibiotics. |
Section 7 of 7Exam technique
1
Saying bacteria 'become used to' antibiotics. Resistant bacteria arise by mutation and are selected.
2
Claiming people become resistant. It is the bacteria that become resistant.
3
Writing that antibiotics treat colds or flu, which are viral.
4
Stating that painkillers cure infections. They only reduce symptoms.
5
Stopping the course early because you feel better. Some bacteria may still be alive.