Biology – Natural and artificial selection | e-Consult

Antibiotic resistance arises through a process driven by natural selection. Initially, within a bacterial population, there will be inherent genetic variation. Some bacteria may possess genes that confer some level of resistance to a particular antibiotic, even if it's only a slight advantage. When an antibiotic is introduced, it will kill off the majority of the bacteria that are susceptible.

This creates a selective pressure – the antibiotic acts as the selective agent. The bacteria with resistance genes are more likely to survive and reproduce. Because they survive, they pass on their resistance genes to their offspring. Over successive generations, the proportion of resistant bacteria in the population will increase. This is because the resistant bacteria have a higher fitness in the presence of the antibiotic. Eventually, the population may consist almost entirely of antibiotic-resistant bacteria. This is a clear example of natural selection – the environment (presence of the antibiotic) favors individuals with traits (resistance genes) that enhance their survival and reproduction.

The process can be further accelerated by the overuse and misuse of antibiotics, which increases the frequency of selection events and provides more opportunities for resistant strains to emerge and proliferate.