You have now met bacteria, viruses, protists and fungi. Together they are called microbes. People mostly hear about the harmful ones, but those are a small share.
Key idea
Microbes make foods like yogurt, cheese and bread, recycle nutrients, and live in our bodies. A few cause disease. Different microbes are different kinds of life, so the medicine that acts on one may do nothing to another: antibiotics act on bacteria, not viruses.
| Illness | Caused by |
|---|---|
| Strep throat | A bacterium |
| Tuberculosis | A bacterium |
| Common cold, flu, chickenpox | Viruses |
| Athlete's foot, ringworm | Fungi |
| Malaria | A protist, carried by mosquitoes |
Why it works
Antibiotics work by damaging parts that bacterial cells have, such as their walls or ribosomes. Viruses have none of these parts, so antibiotics cannot touch them. Washing hands with soap and water removes many germs of all kinds, because soap lifts microbes off the skin so water can rinse them away (CDC).
Worked examples
Worked example: Match the medicine
Could an antibiotic act on what causes strep throat? On what causes a cold?
- Strep throat is caused by a bacterium: yes.
- A cold is caused by a virus: no.
Answer: Strep throat yes; a cold no.
Worked example: Sort it
Is the mold that makes penicillin helpful or harmful?
- Penicillin is a medicine that acts on many bacteria.
Answer: Helpful.
Common mistake
Thinking every microbe is harmful and that one medicine works on all of them. Most microbes are harmless or helpful, and antibiotics do nothing against a virus. Check: first ask what kind of microbe it is.