What causes antibiotic resistance?

A bacterium resists a medication when the bacterium has changed in some way. The change either protects the bacterium from the action of the medication or neutralizes the medication.

Any bacterium that survives an antibiotic treatment can multiply and pass on its resistant properties. Also, some bacteria can transfer their medication-resistant properties to other bacteria — as if passing along a cheat sheet to help each other survive.

The fact that bacteria develop resistance to a medication is normal and expected. But the way that medications are used affects how quickly and to what extent resistance occurs.