Both ethanol (ethyl alcohol) and isopropanol (isopropyl alcohol) are alcohols that kill bacteria. Alcohols kill bacteria by first making the lipids that are part of the outer protective cell membrane of each bacterium cell more soluble in water so that the cell membrane begins to lose its structural integrity and fall apart. As the cell membrane disintegrates, alcohol can then enter the cell and denature proteins within each bacterium.
Proteins are chains of 20 or more amino acids linked together, which then curl and fold into a particular shape (unique to each type of protein) and are required for the protein to function properly within the cell. Alcohol disrupts the shape of proteins, called denaturing by scientists, so that the protein loses its biological activity and can no longer function.
The different proteins in bacteria participate in many cell functions, including providing swimming movement, stabilizing mating bacteria during DNA transfer, attaching to surfaces, protecting against being engulfed and eaten by phagocytes (such as white blood cells), generating energy and transporting solutes into or out of the cell. The disruption of many of the cell functions necessary for bacteria to live and reproduce causes the bacterium cells to die.