Medicines that fight bacteria
Antibiotics are medicines that kill bacteria or stop them from multiplying. They treat bacterial infections like strep throat, urinary tract infections, pneumonia and infected cuts. Before antibiotics, these infections often killed people.
The discovery of antibiotics
| Year | Event |
|---|---|
| 1910 | Paul Ehrlich (Germany) develops Salvarsan, an early chemical treatment for syphilis |
| 1928 | Alexander Fleming discovers penicillin from a mould |
| 1935 | Gerhard Domagk discovers sulfa drugs (Prontosil) |
| 1940s | Penicillin mass-produced during World War II |
| 1943 | Selman Waksman’s lab discovers streptomycin, the first antibiotic effective against tuberculosis |
| 1940s–1960s | "Golden age": most of today’s major antibiotic classes discovered, many from soil microbes |
| 1987 onward | Very few new classes of antibiotics discovered |
Many antibiotics come from soil fungi and bacteria, which produce them naturally to fight off competing microbes.
How antibiotics work
Antibiotics target parts of bacterial cells that human cells don’t have, so they harm bacteria but not us.
| Target | How it works | Example |
|---|---|---|
| Cell wall | Stops bacteria from building walls; they burst | Penicillin, amoxicillin |
| Protein production | Blocks bacterial ribosomes from making proteins | Tetracycline, erythromycin |
| DNA copying | Stops bacteria from copying their DNA | Ciprofloxacin |
| Cell membrane | Damages the outer membrane | Polymyxins |
| Metabolism | Blocks chemicals bacteria need | Sulfa drugs |
Some antibiotics kill bacteria (bactericidal); others stop them from growing so the immune system can finish the job (bacteriostatic).
Broad and narrow
| Broad-spectrum antibiotic | Narrow-spectrum antibiotic |
|---|---|
| Works against many kinds of bacteria | Targets specific bacteria |
| Useful when the cause is unknown | Less harm to helpful bacteria |
| Can disrupt gut bacteria | Preferred when the bacterium is known |
What antibiotics can’t do
Antibiotics do not work on viruses. Colds, flu, most sore throats, most coughs and COVID-19 are caused by viruses. Taking antibiotics for them won’t help and can cause harm.
Side effects
Antibiotics can kill helpful bacteria too, especially in the gut. Side effects can include:
- upset stomach or diarrhea
- yeast infections
- allergic reactions (some severe)
Antibiotic resistance
Antibiotic resistance is one of the biggest threats to global health. The World Health Organization lists it among the top global public health threats.
How resistance develops
- Bacteria multiply quickly, and random mutations happen.
- A few bacteria happen to have genes that let them survive an antibiotic.
- When the antibiotic is used, the others die, but these survive and multiply.
- Bacteria can also share resistance genes with each other.
- Soon, the antibiotic no longer works.
This is natural selection, happening fast.
Superbugs
Superbugs are bacteria resistant to several antibiotics.
| Superbug | Concern |
|---|---|
| MRSA | Resistant Staphylococcus aureus; skin and blood infections |
| Drug-resistant tuberculosis | Much harder and longer to treat |
| Resistant gonorrhea | Few treatment options remain |
| CRE | Resistant gut bacteria; very hard to treat |
Antimicrobial resistance was directly responsible for over a million deaths worldwide in 2019, and contributed to millions more.
What causes resistance to spread?
- Taking antibiotics for viral infections
- Not finishing a prescribed course
- Sharing or saving leftover antibiotics
- Heavy use of antibiotics in farm animals
- Poor infection control in hospitals
Fighting resistance
| Action | Who |
|---|---|
| Take antibiotics only when prescribed | Patients |
| Take them exactly as directed | Patients |
| Prescribe only when needed | Doctors |
| Wash hands and keep vaccines up to date | Everyone |
| Reduce antibiotic use in agriculture | Farmers and governments |
| Develop new antibiotics and alternatives | Scientists |
Scientists are exploring new approaches, including phage therapy (using viruses that attack bacteria) and using artificial intelligence to discover new antibiotic molecules.
Common mistakes
- Using antibiotics for colds and flu.
- Stopping early when you feel better without asking a doctor.
- Thinking people become resistant. Bacteria become resistant.
Try it yourself
- Make a two-column chart: illnesses caused by bacteria and illnesses caused by viruses.
- Simulate resistance: start with 20 beads (18 white, 2 red = resistant). "Treat" by removing most white beads each round, then double the remaining beads. What happens after five rounds?
- Design a poster encouraging people to use antibiotics wisely.
Quick recap
- Antibiotics kill bacteria or stop their growth by targeting bacterial structures.
- Penicillin was the first widely used antibiotic; many came from soil microbes.
- Antibiotics don’t work on viruses.
- Misuse leads to antibiotic resistance and superbugs.
- Using antibiotics wisely helps keep them working.