Salt prevents the growth of microorganisms on the meat because it creates an environment of high salinity in which the microorganisms can not survive. The high concentration of salt on the meat creates a steep concentration gradient of Na+ and Cl- ions across the cellular membrane of microorganisms. In other words there is a higher concentration of salt outside of the microorganisms than in the cytoplasm. This results in water moving out of the cell as it moves down it’s concentration gradient (this is osmosis). Large amounts of water leave the cytoplasm of the microorganism, killing it.