The widespread use of antibiotics for the treatment of bacterial infections has led to the development of antibiotic resistance in some species of bacteria - HSC - SSCE Biology - Question 19 - 2003 - Paper 1

Antibiotic resistance in bacteria is primarily the result of natural selection, a fundamental mechanism of evolution. When antibiotics are introduced, they create a selective pressure that favors bacteria that have or can acquire resistance mechanisms.

1. Mutation: Spontaneous mutations in bacterial DNA can sometimes result in resistance. For example, a mutation may change the structure of a drug target so that the antibiotic can no longer bind effectively.

2. Gene Transfer: Bacteria can also acquire resistance genes from other organisms through horizontal gene transfer mechanisms such as transformation, transduction, and conjugation. These genes may provide the ability to produce enzymes that degrade antibiotics or change cell permeability to limit drug entry.

3. Population Dynamics: As resistant bacteria survive and reproduce, the frequency of resistance genes increases in the population. Over time, these resistant strains can become dominant, leading to clinical scenarios where conventional antibiotics are ineffective.

In summary, the combination of mutation, gene transfer, and selective pressure from antibiotic use leads to the evolution of antibiotic resistance in bacterial populations.