When a bacterial infection is treated with an antibiotic, the hope is that the antibiotic will kill all of the bacteria and prevent them from reproducing. however, if the full prescription of antibiotics is not taken by the sick person, some of the more resistant bacteria can survive. when they reproduce, these bacteria can pass the genes responsible for their resistance on to their offspring. as a result, subsequent administration of the same antibiotic will be less and less effective over time.