Salt usually slows or stops the growth of bacteria and sometimes kills existing bacteria. Some strains of bacteria, such as Staphylococcus, have evolved to survive in salty environments.
Bacteria require a water-rich environment to survive. Salt dehydrates cells, which can prevent them from reproducing and can even kill them. A concentration of 20 percent salt is usually sufficient to kill bacteria. Staphylococcus is one exception to this rule, however. High enough concentrations of salt still kill it, but it can survive at much higher concentrations than other strains of bacteria. Some other types of bacteria, including cyanobacteria, are also unusually tolerant of salt.