Bacteria mutate in order to adapt to new conditions. A mutation that enables a microbe to survive in the presence of an antibiotic quickly spreads throughout a microbial population. Since bacteria replicate very rapidly, a mutation can swiftly become prevalent. The overuse of antibiotics promotes the emergence of resistant bacteria. Antibiotics may sometimes be prescribed for viral infections, but they are not effective against such infections. Furthermore, patients often fail to follow the directions for taking antibiotics precisely. A prescribed dose of antibiotics should be taken until the course is completed. Although an individual can feel better shortly after starting a treatment, not completing the full course of antibiotics often destroys only the most vulnerable bacteria. Relatively resistant bacteria are able to survive and prosper in a human’s body. Because antibiotic-resistant strains of bacteria do not respond to standard treatments, illnesses are able to last for longer periods of time and can result in death. The proliferation of resistant bacteria has made it more difficult to establish effective treatments.