Cambridge O Level Biology · Syllabus 5090 · Inheritance
Antibiotic Resistance
What is Antibiotic Resistance?
The ability of some bacteria to survive treatment with an antibiotic that kills other members of the same species. Resistance arises from a random mutation, which occurs independently of whether the antibiotic is present. When the antibiotic is used it acts as a selection pressure: bacteria without the resistance allele are killed or reproduce less, while resistant bacteria survive and reproduce, passing the allele to their offspring. The proportion of resistant bacteria in the population therefore rises and the antibiotic becomes less effective against it. This is natural selection acting on a bacterial population, not a change produced in individual bacteria by the antibiotic.
This definition is part of the Inheritance chapter in Cambridge O Level Biology.