A chef sprays antimicrobial cleaner on her counter top. At the first, the bacteria population declines significantly. However, even though she continues to spray in following weeks, the number of bacteria begins to increase again. Why did this happen? After the application of antimicrobial spray, the bacteria needed to adapt by developing antimicrobial spray-resistant traits. Some bacteria had traits that allowed them to survive the initial antimicrobial application. They produced offspring also carrying those traits. The antimicrobial compound caused a mutation for resistance to it. This trait increased in the population over time. The bacteria that tried hardest to become resistant left more offspring, who were also resistant.