Bacteria evolution

Every time an organism reproduces, there is a chance of mutations, the raw material for evolution. Fast-reproducing organisms like bacteria have high rates of evolution.

Selection pressure

One force that drives evolution is selection pressure, which results from an environmental factor that strongly affects an organism. Since antibiotics kill normal bacteria or prevent their reproduction, they exert tremendous selction pressure.

Antibiotics resistance

Occasionally a chance mutation may occur that gives a bacterial cell the ability to survive exposure to antibiotics. When antibiotics are used against bacteria, any cells with this mutation will survive longer than other bacterial cells.

Antibiotics overuse

Every time antibiotics are used, there is a chance for resistant bacteria to evolve. Using these drugs when they are not necessary can increase the rate of bacteria evolution.

Antibiotics misuse

Sometimes bacteria are only partially resistant to antibiotics and will still die after prolonged exposure. Shortened exposure allow them to survive and perhaps evolve even greater resistance the next time antibiotics are used. Antibiotics should always be used for the entire time prescribed.

Source:

"Evolution and spread of antibiotic resistance;" B. Henriques Normark & S. Normark; Journal of Internal Medicine 2002; 252(2):91-106

"Antibiotic Resistance Questions & Answers;" Centers for Disease Control and Prevention (CDC)

More Information:

"Antibiotic Resistance;" FamilyDoctor.org