How does alcohol kill bacteria?

Answer:

Highly concentrated amounts of alcohol (70% and higher) can kill bacteria by damaging the plasma membrane and denaturing proteins within the cell.

Gram-negative bacteria are more vulnerable to alcohol because they contain a thin peptidoglycan cell wall covered by an outer membrane. The outer membrane controls the passage of substances into and out of the cell. Alcohol dissolves the outer membrane. This allows substances that are normally blocked by the membrane to easily enter the cell through the thin peptidoglycan cell wall. In addition, cell contents leak out of the cell through the cell wall.

Gram-positive cells lack outer membranes and rely solely on thick peptidoglycan cell walls to protect them from the environment but can still be killed by alcohol.