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Medical Science
Antibiotic Resistance
Why Superbugs Evolve
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Antibiotic resistance occurs when bacteria evolve ways to survive medicines that once killed them or stopped their growth. It matters because common infections can become harder, more expensive, and more dangerous to treat. Resistant infections such as MRSA, CRE, and drug-resistant tuberculosis can spread in hospitals and communities. This problem also threatens surgeries, organ transplants, and cancer treatments, where preventing infection is essential.
Key Facts
- Antibiotics kill susceptible bacteria, but resistant bacteria can survive and reproduce.
- Selection pressure increases when antibiotics are overused, misused, or stopped too early.
- Resistance can arise by mutation: a random DNA change may help a bacterium survive an antibiotic.
- Bacteria can share resistance genes on plasmids through horizontal gene transfer.
- Growth of bacteria can be modeled as N = N0 x 2^n, where n is the number of generations.
- Stewardship reduces resistance by using the right antibiotic, dose, duration, and only when needed.
Vocabulary
- Antibiotic
- A medicine that kills bacteria or slows their growth, but does not treat viral infections.
- Antibiotic resistance
- The ability of bacteria to survive exposure to an antibiotic that would normally kill them or stop their growth.
- Selection pressure
- An environmental factor, such as antibiotic exposure, that favors organisms with traits that help them survive.
- Plasmid
- A small circular DNA molecule in bacteria that can carry genes, including antibiotic resistance genes.
- Stewardship
- The careful use of antibiotics to treat infections effectively while slowing the spread of resistance.
Common Mistakes to Avoid
- Using antibiotics for colds or flu is wrong because these illnesses are usually caused by viruses, and antibiotics target bacteria, not viruses.
- Stopping antibiotics as soon as you feel better can be wrong because some bacteria may remain alive and the more resistant survivors can multiply.
- Thinking the human body becomes resistant is wrong because the bacteria evolve resistance, not the patient’s cells.
- Assuming stronger antibiotics are always better is wrong because unnecessary broad-spectrum drugs can kill helpful bacteria and increase selection for resistant strains.
Practice Questions
- 1 A culture starts with 500 bacteria. After treatment, 2 percent are resistant and survive. How many resistant bacteria remain?
- 2 A resistant bacterium divides once every 30 minutes. Starting with 1 resistant bacterium, how many bacteria are present after 5 hours if none die?
- 3 Explain why using antibiotics only when needed can slow the evolution and spread of resistant bacteria.