Antibiotics are used to control diseases caused by bacteria in humans and animals. The antibiotics mimic the normal food of the bacteria, and upon ingestion, the bacteria are killed. However, there have been increasing problems of bacteria showing resistance to our common antibiotics.

The graph above shows that the bacteria naturally have genes which show a lot of variation in terms of resistance to the antibiotic. Those at the left are easily killed by the antibiotic, while those at the right are only completely killed by higher antibiotic dosages.