Antibiotics do not cause resistance mutations, but they select for bacteria that already carry them. This is natural selection:
1. A population of bacteria shows variation. A few cells carry an allele for resistance, which arose by chance mutation.
2. When the antibiotic is used, it acts as a selection pressure. Susceptible bacteria are killed or stop dividing.
3. Resistant bacteria survive and, with less competition, reproduce rapidly.
4. They pass the resistance allele on to their offspring, and to other bacteria by conjugation.
5. Over many generations the frequency of the resistance allele increases until most of the population is resistant.
Because bacterial generation times are short, this can happen within weeks.Human activities that speed this up:
• overprescribing, including giving antibiotics for viral infections, where they have no benefit;
• patients not completing the course, so the most resistant bacteria are the ones left alive;
• using broad-spectrum antibiotics when a narrow-spectrum one would work, exposing more species;
• widespread use in farming, for example to prevent disease in intensively kept animals;
• poor hygiene in hospitals, allowing resistant bacteria to spread between patients.Reducing the problem. Doctors should prescribe antibiotics only when needed, identify the pathogen and choose a narrow-spectrum drug, and sometimes use two antibiotics together, since a bacterium is unlikely to be resistant to both. New antibiotics are also being developed, but few new types have been found in recent decades.
1. A population of bacteria shows variation. A few cells carry an allele for resistance, which arose by chance mutation.
2. When the antibiotic is used, it acts as a selection pressure. Susceptible bacteria are killed or stop dividing.
3. Resistant bacteria survive and, with less competition, reproduce rapidly.
4. They pass the resistance allele on to their offspring, and to other bacteria by conjugation.
5. Over many generations the frequency of the resistance allele increases until most of the population is resistant.
Because bacterial generation times are short, this can happen within weeks.Human activities that speed this up:• overprescribing, including giving antibiotics for viral infections, where they have no benefit;
• patients not completing the course, so the most resistant bacteria are the ones left alive;
• using broad-spectrum antibiotics when a narrow-spectrum one would work, exposing more species;
• widespread use in farming, for example to prevent disease in intensively kept animals;
• poor hygiene in hospitals, allowing resistant bacteria to spread between patients.Reducing the problem. Doctors should prescribe antibiotics only when needed, identify the pathogen and choose a narrow-spectrum drug, and sometimes use two antibiotics together, since a bacterium is unlikely to be resistant to both. New antibiotics are also being developed, but few new types have been found in recent decades.