Pickles are often preserved in a 20-30% salt solution called brine. how does this method prevent contamination by microorganisms?

The salt solution (brine) is a  hypertonic solution. It means that there is a higher concentration of dissolved salts outside of the cell, and a lower concentration of water than the cell. If the concentration difference is too great, the microorganisms  cannot survive because the cells  will be  dehydrated and soon die,