Understand how resistance to antibiotics can increase in bacterial Population.
An example of this:
Staphlococcus aureus can lead to skin and lung infections.
People with this bacteria can be treated with Methecilline Antibiotics which can kill Staphlococcus aureus. The Staphlococcus aureus that can be killed by this antibiotic is called the susceptible form. MSSA (Methecilline susceptible Staphlococcus aureus).
What happened was there was a random mutation to the geno of Staphlococcus aureus and when the antibiotics Methecilline is applied it doesn't die and this is called the resistant form. (Methecelline Resistant Staphlococcus aureus)
The mutation has created genes that allowed the bacteria to break down the antibiotics, resisting it so it can survive. As antibiotics are used across time this type of bacteria increasingly surivives and becomes more common. In time this has become a serious problem in hospitals.