Evolution of antibiotic resistance in bacterial populations

The evolution of antibiotic resistance in bacterial populations is a direct consequence of natural selection applied by widespread use of antibiotic drugs. When a new antibiotic is first introduced, it kills the vast majority of bacteria exposed to it. The surviving bacterial cells, however, may include individuals whose genomes happen to include a mutant gene that confers resistance. As Darwin understood, individuals carrying the resistance gene will leave behind a disproportionately large share of offspring, which inherit the gene. If the environment consistently contains an antibiotic, bacteria carrying the resistance gene will eventually come to predominate. Because bacteria reproduce so rapidly and have comparatively high rates of mutation, evolutionary change leading to resistant populations is often rapid.

We have accelerated the pace of the evolution of antibiotic resistance by introducing massive quantities of antibiotics into the bacteria's environment. Each year, U.S. physicians prescribe more than 100 million courses of antibiotics; the Centers for Disease Control estimate that about half of these prescriptions are unnecessary. An additional 20 million pounds of antibiotics are fed to farm animals annually. The use of antibacterial soaps and cleansers has become routine in many households. As a result of this massive alteration of the bacterial environment, resistant bacteria are now found not only in hospitals and the bodies of sick people but are also widespread in our food supply and in the environment. Our heavy use (many would say overuse) of antibiotics means that susceptible bacteria are under constant attack and that resistant strains have little competition. In our fight against disease, we rashly overlooked some basic principles of evolutionary biology and are now paying a heavy price.